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Highlights • The microstructural changes of the plugging agent were analyzed during hydration. • The reasons for the hardening effects of each activator were analyzed. • The hydration heat of the reaction between the slag and activators was characterized. Abstract To reduce the amount of time required for the formulation, adjustment, and application of a hardened plugging agent in the field, this study performed an in-depth analysis of the hydration mechanism of a slag-based plugging agent by heat of hydration characterization, transmission electron microscopy, nuclear magnetic resonance, and X-ray photoelectron spectroscopy. The study shows that the NaOH activation of the slag-based plugging agent can produce an intermediate product Ca(OH) 2 that is dissolved continuously to produce OH−, allowing the reaction to proceed continuously. Slag hardening occurs as follows: after the structure is destroyed, the recombination of groups changes their mutual spatial positions, thereby increasing the force between the groups and hardening the slurry. During the hydration process, a certain degree of substitution of Si by nonskeletal-element Al atoms in the slag occurs to form aluminosilicate, promoting the strength development of the slurry structure. The study results reveal a theoretical basis for shortening the time for the formulation and adjustment of the hardened slag-based plugging agent and provide new ideas for the development of new activators. [ABSTRACT FROM AUTHOR]

Highlights • Linear decrease of the geopolymers mechanical strength with the increasing of water. • Small variation of water content leads to significant modification of the porosity. • More than 90% of the geopolymer water are easily removable after hardening. • The drying of geopolymer mortars could lead to a decrease in strength. • Geopolymer presents an interconnected monomodal mesoporosity. Abstract This study assesses the influence of the initial amount of water in metakaolin-based geopolymer on some of its properties in the hardened state. Results suggest a linearly decreasing influence of the amount of water on the mechanical performance of the geopolymer and showed that the majority of this water was not bonded to the structure. Moreover, it was found that whatever the amount of water initially introduced, all the samples contained the same amount of water after a drying period. The study of the porous network showed a large pore volume of 50% of the total volume which corresponds to the volume of water initially introduced. Finally, the observation of numerous macropore helped to explain the high transfer coefficients measured on the geopolymer. [ABSTRACT FROM AUTHOR]

Highlights • 87 research articles on lightweight self-compacting concrete have been reviewed. • Physical properties of LWA which affect the LWSCC performance are reviewed. • Fresh and hardened properties of LWSCC are reviewed. • Features and limitations of 6 LWSCC mixture methods are presented. Abstract The utilization of natural and artificial lightweight aggregates in lightweight self-compacting concrete (LWSCC) is gaining popularity in research field. Extensive research has been carried out in the past decade all over the world to utilize lightweight aggregates (LWA) in self-compacting concrete (SCC). LWSCC, which uses renewable aggregates, has great potential to become an alternative material to conventional concrete. The paper is aimed to review the more recent research of physical properties of lightweight aggregates used in developing mix design of lightweight self-compacting concrete. In design, the mix proportion of LWSCC is a crucial factor to achieve the desired fresh and hardened concrete properties. The methods to develop LWSCC mix design with anticipated fresh and hardened concrete are reviewed. Research shows that the mix design LWSCC is preferably proportioned by aggregates packing concept. In addition, discussion on the fresh and hardened concrete properties is made and summarized in this paper. Studies indicate that there is a promising future for the use of lightweight aggregates in SCC as it shows satisfactory filling ability, passing ability, segregation resistance and compressive strength. Research gaps recommendations are then identified through this review to further discover lightweight self-compacting concrete in several aspects, particularly in term of sustainability. [ABSTRACT FROM AUTHOR]

Highlights • Hemp concrete rigidity is assessed using different methods: floating, cyclic, etc. • Three types of modulus – apparent, elastic and hardening modulus – are determined. • Tendency of floating method to overestimate the modulus values has been highlighted. • It is highlighted that cyclic method tends to underestimate modulus with low values. • Thanks to its low dispersion, the floating method is better suited for such material. Abstract Parameters influencing the variability of Young's modulus for hemp concrete include, among others, the method by which it is calculated. At present, a range of methods are available in the literature, but as yet, little is known about how they might affect the obtained results, given that hemp concrete is a highly sensitive material. For the in-depth study of this issue presented herein, the Young's modulus properties of two formulations of hemp concrete are analysed. Three main types of modulus – apparent, elastic and hardening modulus – are determined, using different calculation methods: floating, tangential, cyclic and hardening with 5 strategies. Therefore, for a stress–strain curve with 3 loading/reloading cycles, a total of 38 modulus values are calculated. Using the aforementioned methods, a comparative study of the results at 60, 90 and 180 days on 5 specimens for each formulation and each age reveals that the cyclic modulus method gives low values and the tangential modulus method gives medium values, while the floating modulus method gives higher values. In this latter case, low dispersion is observed, making this method more suitable to calculate hemp concrete's modulus. [ABSTRACT FROM AUTHOR]

Highlights • Experimental campaign on industrial and experimental thermal renders. • Formulations with EPS, cork, and several binders and admixtures. • Physical properties at fresh and hardened states. • Standard and non-standard specimens and brick-render models. Abstract Nowadays, there is a concern in getting buildings with reduced environmental impact and improved thermal and energy performance. The need to use new technologies to comply with the thermal requirements has been driven by the regulation for buildings. With this goal in mind, the use of thermal insulation systems on facades has increased. In this context, renders with high thermal insulation performance have recently emerged on the market. This paper discusses the physical characteristics of four industrial thermal renders, comparing with two experimental render mixtures in which sand is replaced by aggregates with thermal insulating properties (EPS and cork) without any additions or admixtures. It is noticed a need to incorporate high ratios of aggregate with thermal characteristics to achieve thermal insulation renders, affecting other physical properties of the renders at both fresh (workability, air content and bulk density) and hardened (water absorption under low pressure, capillary, dry bulk density, open porosity and drying capacity) states. [ABSTRACT FROM AUTHOR]

Highlights • HCSP used to replace 0.0–15.0% of cement in preparing cement pastes and mortars. • Adverse effect of HCSP on the rheological behaviour of fresh pastes and mortars. • Optimum percentage of cement substitution is 7.5% maximises mechanical strength. • Increasing HCSP content leads to drying shrinkage increasing and then decreasing. Abstract This paper presents an experimental study on the rheological behaviour and mechanical strength of cement pastes and mortars prepared with high-calcium sepiolite (HCSP). HCSP was used to replace 0.0%, 2.5%, 5.0%, 7.5%, 10.0%, and 15.0% of cement. The rheological behaviour of fresh specimens was investigated along with the yield stress and plastic viscosity, which were approximated using the Bingham plastic model. Tests were also conducted to investigate the compressive strength, flexural strength, and drying shrinkage of hardened specimens. The results showed that the addition of HCSP has an adverse effect on the rheological behaviour of fresh specimens. The compressive strength and flexural strength are highest for specimens with an HCSP content of 7.5% but this is somewhat negated by the high drying shrinkage values. In contrast, the drying shrinkage values are lowest for specimens with the highest HCSP content (15.0%). It can be concluded that HCSP is a potential cement replacement material, but it is necessary to improve the workability of the fresh specimens and reduce drying shrinkage of the hardened specimens before this mineral can be used in the production of structural concrete. [ABSTRACT FROM AUTHOR]

Highlights • Local Hollomon strain hardening exponent (n) values are studied for different rebar steel. • Hardening exponent evolution is related with deformation mechanics. • Strain is characterized in related microestructural features by EBSD studies. Abstract The typical distribution of steel used in developed countries, according to World Steel Association, attributes approximately 35% of total steel production in the world to the construction sector. Rebar steel consumption constitutes a significant proportion of that figure. More in-depth knowledge regarding the behaviour of steels used in the production of rebar would be advantageous. It has been shown that elasto-plastic behaviour greatly affects the behaviour of steel under seismic action. In particular, the engineering strain at maximum engineering stress, A gt , is gaining importance as the key ductility parameter in the latest standards. Several authors have linked the value of A gt to the Hollomon strain-hardening exponent, n. Three materials have been tensile tested at room temperature, namely TEMPCORE® carbon steel, an austenitic, and duplex steel. In this paper, it is shown that such a link is only valid when the local n value is computed at A → A gt (ε z → ε gt in true values). In accordance with the metallographic structure of rebar, the contrasting behaviour of the Hollomon strain-hardening exponent n versus ε z is described. [ABSTRACT FROM AUTHOR]

Highlights • Concrete mixtures with low PC may be designed through the use of continuous PPMs. • Alfred PPM seems able to design low cement concrete with suitable fresh properties. • Alfred PPM may design low cement concrete with interesting hardened properties. • Inert fillers help reducing PC in concrete, keeping fresh and hardened properties. • Long-term performance of low PC concrete still needs further investigation. Abstract Concrete, the major construction material used in the construction industry worldwide, presents a huge environmental impact producing about 7% of the global carbon dioxide. Given the concerns related to global warming, studies have been focusing on distinct approaches aiming to reduce the amount of Portland cement (PC), which is the least sustainable ingredient of the mixture, by adopting alternative mix-design strategies such as the use of particle packing models (PPMs). However, there is currently a lack of data on the efficiency of the use of continuous PPMs to reduce PC while maintaining or improving concrete fresh and/or hardened properties. This work aims to investigate the impact of current and modified versions of continuous PPMs on the fresh (rheological behaviour) and hardened (compressive strength, modulus of elasticity, porosity, and permeability) state of mixtures designed with low and moderate amounts of PC. Results demonstrate that eco-efficient concrete may be produced through current and modified continuous PPMs without compromising the fresh and hardened properties of the material. Nevertheless, further durability and long-term investigations must be performed on systems with reduced PC contents. [ABSTRACT FROM AUTHOR]

Highlights • The relationship between SCC and its corresponding suspending phase was evaluated. • The rheological properties of sieved and modified mortars are well correlated. • The VP/VS, W/B, and suspending phase affect the intrinsic viscosity. • The proposed modified models were extended to predict rheological properties. Abstract Understanding the rheology of self-consolidating concrete (SCC) is a key step to ensuring proper flow and successful casting in formworks, and hence good performance of the hardened material. The rheology of SCC is a function of several mixture parameters, including water-to-binder ratio (W/B), paste content, coarse aggregate content and grading, and presence of chemical admixtures. The mix design of SCC is less robust than conventional concrete and necessitates vigorous optimization to ensure adequate flow performance. The research emphasis in this study is on developing a practical approach that can be used to predict rheological properties of SCC as a diphasic material, which will contribute significantly to simplifying the protocols for mixture optimization and material selection. Various SCCs and their corresponding mortar mixtures were investigated covering a wide range of mixture proportion parameters, including W/B, paste-to-sand volume (VP/VS), and coarse aggregate (CA) type and content. The rheological properties of SCC, mortar phases, and the relationship between the two phases are evaluated and discussed in this paper. Test results show very good correlation between the rheological properties of modified design mortar, sieved mortar, and SCC mixtures. Prediction adequacy was mostly affected by VP/VS and W/B parameters. Modified Krieger–Dougherty (KD) and Chateau–Ovarlez–Trung (COT) models satisfactorily predicted the rheological properties of SCC mixtures. [ABSTRACT FROM AUTHOR]

Highlights • Mixes achieve 90% of their one year flexural strength at the age of one day. • RCSF enhances flexural strength and toughness resulting in hardening behaviour. • Constitutive equations of RILEM & MC recommendations overestimate loading capacity. • FEA analysis using multilinear σ-ɛ tensile curves capture post cracking strength. Abstract To minimise disruption due to repairs of concrete pavements, rapid hardening and tough materials need to be used. This paper investigates the flexural performance of rapid hardening mortar mixes made with two commercial cement types, calcium sulfo-aluminate cement and calcium aluminate cement, for thin concrete repair applications. Three-point bending tests are performed on plain and steel fibre reinforced concrete specimens containing 45 kg/m3 of recycled clean steel fibres to characterise the flexural performance of notched and unnotched prisms at different ages, ranging from one hour up to one year. The recycled fibers are shown to enhance both the flexural strength and toughness of FRC prisms, leading to hardening behaviour. Constitutive equations based on the RILEM and Model Code 2010 recommendations are found to overestimate the loading capacity of the bending tests. FE analyses using multilinear σ-ɛ tensile curves obtained by employing inverse analysis can capture better the post cracking strength and cracking pattern of the tested prisms. [ABSTRACT FROM AUTHOR]

Highlights • Effects of polymer on the microstructure evolution and strength development were examined from 2 h to 90 days. • Increasing the polymer proportion up to 10% delayed the setting and hydration and reduced the early strength. • The long-term strengths of mortars exhibited convergence regardless of the polymer ratio. • The polymer addition induced the formation of more ordered and denser ITZs between the mortar and coarse aggregate. Abstract Ultra rapid hardening (URH) cement is used where ultra high early strength is required in construction. This study investigated the age-dependent characteristics of calcium sulfoaluminate (CSA)-based URH cement modified by the addition of acrylic redispersible polymer powder. Specifically, the effects of polymer powder on the microstructure evolution and strength development were examined from an early age of 2 h up to 90 days. The macro- and microstructural properties of various cement paste, mortar, and concrete samples were characterized by compressive strength, rheology, mercury intrusion porosimetry, powder X-ray diffraction, and scanning electron microscopy with energy-dispersive spectroscopy. The test results revealed that increasing the polymer proportion up to 10% by mass of cement not only delayed the setting and hydration, but also refined the pore structures of the URH cement systems, which is considered the main cause of the long-term strength convergence of the mortars with different polymer ratios. The polymer addition induced the formation of more ordered and denser ITZs between the mortar and coarse aggregate. All findings support the favorable effects of the polymer powder on the long-term strength and durability of the URH cement systems. [ABSTRACT FROM AUTHOR]

Highlights • A small amount (0.25%) of fiber showed a positive influence on compressive strength. • Fiber length (FL) and volume (FV) contributed equal amount (40%) to concrete slump. • Jute fiber showed no significant impact on the split tensile strength of concrete. • FL, FV & their interaction contributed 17, 36 & 47% to flexural tensile strength. Abstract The purpose of this study is to evaluate the addition of jute fibers on the fresh and hardened properties of concrete. Locally produced jute fibers having two different lengths of 10 mm and 20 mm and four different volumes of 0.00%, 0.25%, 0.50%, and 1.00% were added to prepare concrete cylinders and beams. The cylinder specimens were tested for the compressive strength at 7, 28 and 90 days and for the split tensile test at 28 and 90 days, whereas the beam specimens were assessed for the flexural tensile strength at 28 days. Additionally, various factorial analyses were conducted on the experimental results to detect the effect of the volume and size of jute fibers on concrete properties. The experimental results revealed that the addition of 0.50% jute fiber had an adverse impact on the fresh properties of concrete. However, a smaller dosage (0.25%) of jute fiber showed a positive influence on the hardened properties of concrete. The results obtained from factorial analysis demonstrated that the fiber length and volume showed a positive influence on hardened concrete properties at early and extended curing ages, respectively. [ABSTRACT FROM AUTHOR]

Highilights • Mechanical properties of composite during long-term hardening period increase. • Changes of properties are caused by continuing hydration and carbonation procesess. • Hydration and carbonisation depends from Al 2 (SO 4) 3 and Ca(OH) 2 ratio with cement. • Qualitative analysis of the composite composition is conducted using X-ray and DTA. Abstract Fibre Hemp Shiv (FHS) is one of the most widely used bio-aggregates for the development of eco-friendly building materials. Research on composites with an FHS aggregate has usually been limited to short-term property analyses that depend on the type of binder. Such properties are determined after (7–90) days of curing. Most scientists have focused on researching composites with lime (L) based binders. This work focuses on composites with a cement (CEM) binder and FHS aggregate, and investigates the impact of long-term curing (for 1 year) on the physical properties (density, compressive strength and thermal conductivity) of composites with non-treated and mineralized FHS (mineralization is performed with aluminium sulphate (AS) and hydrated lime (L)). In order to determine the causes of the changes in properties during long-term curing, changes in the mineralogical composition are analysed. X-ray diffraction, differential thermal and thermogravimetric analyses as well as research on the microstructure of the composites are implemented. The lowest change in properties due to inhibition of hydration is determined for composites with a non-treated aggregate. Mineralized aggregates are characterized by lower cement hydration capability over a long-term period. The change of properties after 1 year of curing depends on the AS/CEM ratio. For all 1-year cured composites, there is a reduction in the peak intensities of C 2 S, C 3 S and ettringite, whereas there is an increase in the peak intensities of calcite, (except for composition with the highest AS/CEM ratio – AS30L18), Calcium Silicate Hydrate (CSH) and portlandite (except for the non-mineralized composition). Lower ratios for AS/CEM (AS18L36 and AS21L42) and, respectively, higher L/CEM ratios in compositions lead to the formation of vaterite. In addition, the above-mentioned composition has the highest L/CEM ratio, which ensures that more hydrates participate in the carbonation process, thus leading to higher compressive strength, denser composite structure and higher thermal conductivity due to higher heat transfer by conduction. [ABSTRACT FROM AUTHOR]

Highlights • High temperature effect on dynamic behavior of concrete was simulated at meso-scale. • The failure process and failure mode of concrete can be can accurately simulated. • Temperature degradation of concrete is more dramatic than strain rate hardening. • The natural cooling process further degenerate the mechanical properties of concrete. • Temperature degrades the elastic modulus of concrete more than compressive strength. Abstract In the present study, considering the internal heterogeneity of concrete, a meso-scopic simulation method was established to explore the dynamic compressive behavior of heterogeneous concretes at and after elevated temperature. In the meso-scale numerical model, the concrete was regarded as a tri-phase composite material consisting of aggregate, mortar matrix and the Interfacial Transition Zones (ITZs). Both the high-temperature degradation effect and the strain rate enhancement effect of the meso-components were taken into account. The simulation method involved two steps: (1) the heat conduction behavior was simulated initially; and (2) using the "result output" as "initial conditions", the dynamic mechanical behavior of concrete was simulated. Based on the great agreement between numerical simulation results and the experimental observations, the dynamic uniaxial compression failure behavior and meso-scale failure mechanism of concrete at and after elevated temperature were studied. Furthermore, the effect of high temperature on the macroscopic dynamic compressive strength and elasticity modulus of concrete were revealed. The results indicate that the concrete specimen still shows significant strain rate effect at and after elevated temperature while the mechanical properties of concrete specimens after natural cooling further degenerates comparing with those at elevated temperature. [ABSTRACT FROM AUTHOR]

Highlights • The highest strength was obtained with TETA hardener, which has six functionalities. • Monofunctional diluent reduced the compressive strengths of TETA and MXDA mortars. • The addition of a diluent into epoxy mortars improved their flexural strength. • The highest adhesion strength was obtained with MXDA hardener and DGEBA resin. • Moderate to poor chemical resistance against formic and lactic acids were obtained. Abstract Three epoxy resins and three types of glycidylether-based reactive diluents were used together in epoxy mortars. Six different amine-based hardeners, four aliphatic and two cycloaliphatic, were used in the mixtures. Test results showed that a hardener with higher functionality results in mortars with higher strength. The combination of diluent and hardener was found to affect both the compressive and flexural strengths of the mortars. The adhesion strengths of the mortars (to a sand-blasted concrete surface) were obtained by pull-off test. It was found that lactic and acetic acids have different levels of destruction in the epoxy mortars. [ABSTRACT FROM AUTHOR]

Highlights • Short sisal fiber reinforced concrete (SSFRC) shown a deflection hardening behavior. • Recycled aggregates had not influence on the cracking and maximum flexural stress. • SSFRC blocks shown higher strength and ductility than commercial solutions. • Slabs with SSFRC blocks presented higher stiffness than slabs with the other blocks. • The numerical analysis shown good agreement with experimental results. Abstract This work is dedicated to the assessment of the structural performance of a new lightweight block for one-way precast concrete slabs made of short sisal fiber reinforced concrete (SSFRC) containing natural and recycled aggregate. The influence of the sisal fibers and recycled aggregate on the physical and mechanical properties was assessed experimentally, with clear benefits of fiber reinforcement on the post-cracking flexural capacity, while the higher water absorption of recycled aggregates had favorable impact on the compressive strength mainly in the FRC. Flexural tests were carried out on SSFRC blocks, as well as on ceramic and expanded polystyrene (EPS) blocks used commercially. The SSFRC blocks presented higher load and deflection capacity with much more ductile behavior, and with a geometry favorable for the passage of infrastructures. Slab panels including SSFRC, ceramic and EPS blocks were tested under four point bending configuration to assess the benefits of the new SSFRC block in quasi-real slab conditions. The results of these tests demonstrated the best structural performance of the SSFRC blocks over the other considered commercial solutions, not only in terms of initial stiffness, but also for the load at serviceability limit deflection conditions (average increase of 23%) and yield initiation (average increase of 38%); The observed continuous crack pattern crossing the SSFRC blocks and the main precast RC beams demonstrated the potentialities of these blocks to contribute for the structural performance of this type of slabs. Material nonlinear finite element simulations were carried out to derive, by inverse analysis, the values of the fracture mode I parameters of SSFRC. This multidirectional smeared crack model was also used to simulate the behavior of the composite materials and the SSFRC blocks, and the obtained level of accuracy has demonstrated the adequacy of the adopted inverse analysis strategy. A Finally, a parametric study was carried out to preview the potentialities of these new SSFRC blocks for this structural application, having been verified that a SSFRC block of 12 mm thickness and 250 mm height, of about 10 kg, is capable of accomplishing the standard recommendations, constituting a competitive and efficient solution for this market segment. [ABSTRACT FROM AUTHOR]

Highlights • Image analysis can determine air content of hardened concrete. • Air entrainment improved workability. GP inclusion impaired workability. • GP inclusion reduced entrained air content, increased trapped air content. • High strength frost resistant concrete can be produced by inclusion of GP and AEA. Abstract Study investigates the influence of ground pumice (GP) addition on compressive strength and air content of air entrained and non-air entrained concrete. Control Portland cement concrete was prepared by keeping the binder amount at 400 kg/m3 with water binder (W/B) ratio 0.45. Air entrained Portland cement concrete mixtures were also prepared by addition of 0.025%, 0.05% and 0.075% air entraining agent (AEA) dosages to control Portland cement concrete. All Portland cement concretes mixtures were modified by inclusion of 10%, 15%, 20% and 25% GP as cement replacement in mass basis, and then concretes containing ground pumice were obtained. Air contents of all fresh concretes were measured. Entrained air void area values on cut surface of hardened concrete were determined by image processing technique. Increase in air entraining agent dosage content in fresh concrete exhibited an increase not only in air content but also flow diameter value of fresh concrete. Addition of ground pumice as a cement replacement in concrete caused reduction in air content and flow diameter, however, it increased compressive strength of air entrained concrete. Compressive strength values related inversely with the air contents of fresh concrete as well as air void area values of hardened concrete computed by image processing technique. Air contents of fresh concrete and image processing void area values of hardened concrete has shown a good relationship between themselves. Image processing can be used to measure air content of hardened concrete. [ABSTRACT FROM AUTHOR]

Highlights • A new hardened cement-bentonite grouting material (HCBGM) for underwater karst cavern was proposed. • Effects of compositions on performances of the HCBGM are investigated. • Optimal formulation of HCBGM for karst cavern with groundwater flow was determined. • The technique, cost and eco effectiveness of the HCBGM was verified by an field case study. Abstract Grouting is one of most important techniques for underwater tunnelling in karst ground which is actually difficult to be resolved due to the presence of underground water flow. This paper proposed a new grouting material to fill karst caverns when there is flowing underground water prior to shield tunnel construction. The grout uses bentonite and cement as the base material, and a curing agent were added to form excellent fluidity, stability and scour resistance. The effects of the composition and formulation on the performance of the grouting material, and the optimal formulations were determined through a series of laboratory experiments. The recommended parameters for the grout are a specific gravity for the bentonite slurry from 1.30 to 1.35, a cement content of 30%, a meta-aluminate content of 1.25% and a lignin content of 0.20%. The effectiveness of the hardened cement-bentonite grouting material (HCBGM) was checked by a field grouting application for a underwater shield tunneling in karst area, and the results illustrated that the proposed grouting material not only can fulfill the engineering requirements but also turns out cost effective and eco-friendly. [ABSTRACT FROM AUTHOR]

Highlights • Additives can be used via four mechanisms to enhance concrete freeze-thaw durability. • Despite strength reduction, air bubbles decrease water pressure within ice formation. • Less permeability and better pore refinement is achieved by consolidation mechanism. • Bridging effect provided by fibers and nanoparticles can control crack propagation. • Applying hydrophobic admixtures could reduce the ice formation in internal surfaces. Abstract Frost resistance is an important factor that can affect the durability of structural concrete. This paper reviews previous studies on freeze-thaw resistance of concrete from the mechanism viewpoint. Observations have revealed that concrete additives can be utilized via different mechanisms to enhance concrete freeze-thaw durability. There are four mechanisms contributing frost resistance: (a) providing extra space for ice expansion in concrete using air bubbles, (b) reducing the porosity of concrete using pozzolans and fillers, (c) containing crack propagation using microfibers, nanotubes and nanosheets, and (d) decreasing water absorption using hydrophobic agents. Each mechanism has been discussed profoundly. However, future investigations are needed to provide a better insight into the grey areas, especially in nanoscale additives and hydrophobic concrete. Researchers should devote more investigations to integrate experiments and extract optimum conditions and dosages for the discussed additives. [ABSTRACT FROM AUTHOR]

Highlights: • Effects of fibre content and characteristics on properties of FRC studied. • Correlations to various fibre factors identified the governing fibre factors. • Traditional practice of taking fibre factor as V f (L/D) is overly simplistic. • Fibre number has been found to be more fundamental than fibre volume. Abstract The concrete mix design of fibre reinforced concrete (FRC) is still largely carried out by a trial and error process of repeatedly conducting trial concrete mixing. Such trial and error process is very slow and sometimes frustrating because the required performance may not be achieved even after many trials. In this study, the effects of the fibre content and characteristics on the fresh and hardened properties of steel FRC have been evaluated by testing and the measured properties have been correlated by regression analysis to the various fibre factors to identify the fibre factor governing each performance attribute. The correlations revealed that the traditional practice of taking the fibre factor as the fibre volume times the aspect ratio is overly simplistic and that the fibre number is more fundamental than the fibre volume. Moreover, based on the correlations, design equations for predicting the various performance attributes have been derived for the mix design of steel FRC. [ABSTRACT FROM AUTHOR]

Highlights • HSC mix design considering curing temperature and duration is proposed. • A method for predicting HSC strength after steaming and normal hardening is proposed. • Good correlation between the calculated and experimental values was obtained. Abstract The paper deals with experimental results on temperature and curing duration influence on strength properties of high strength concrete (HSC). Dependences for calculating strength of high strength concrete at 12 h, 1, 7 and 28 days are developed for normal hardening conditions. Equations, allowing considering curing temperature in diapason between 5 and 40 °C as well as curing duration are proposed. The influence of steam curing parameters on HSC strength characteristics is investigated. Methodology for predicting concrete strength after steam curing and further normal hardening is proposed. The obtained calculation dependences and experimental-statistical models provide wide possibilities for design of effective high strength concrete compositions. [ABSTRACT FROM AUTHOR]

Highlights • Use CO 2 to treat harden cement powder as a supplemental cementitious material. • The incorporation of carbonated cement powder enhances the compressive strength. • Replacement of cement with carbonated cement powder shows a denser microstructure. Abstract Recovering aggregates from recycled concrete produces a large amount of powder, which contains hardened cement paste and is classified as a corrosive hazardous material. This study used CO 2 to treat hardened cement paste powder and to investigate how the incorporation of uncarbonated and carbonated hardened cement paste powder into cement affects the hydration and microstructure development of cement. Carbonated hardened cement paste powder consists mainly of calcite and silica gel. Replacement of cement by uncarbonated cement paste powder content from 10 to 30% by the mass of cement decreases, while replacement of cement with 10–20% carbonated hardened cement paste powder increases the strength of cement up to 90 days. The replacement of cement with 30% carbonated waste paste powder slightly decrease the strength of the cement. The silica gel in carbonated hardened cement paste powder quickly reacts with calcium hydroxide and results in the formation of more C-S-H. The presence of calcite in carbonated hardened paste powder leads to the formation of calcium aluminate hemi-carbonate (CAHC) and calcium aluminate mono-carbonate (CAMC) thus to a stabilization of ettringite (AFt) compared with the control cement paste, in which portion of AFt converts to mono-sulphoaluminate. CAHC is less stable than CAMC and transforms to CAMC in about one week after its formation. These chemical actions lead to a lower porosity and a higher compressive strength for cement paste with carbonated hardened paste powder compared with the control cement paste. [ABSTRACT FROM AUTHOR]

Highlights • We studied utilization of different amount and length of basalt fibre in SCC. • Effect of basalt fibre on the fresh and hardened properties of SCC was investigated. • The addition of basalt fibre in SCC decreases the workability. • Utilization of basalt fibre improves the mechanical properties of SCC. • The optimum values of fibre content and length were determined using RSM. Abstract The use of basalt fibre in the production of self-compacting concrete (SCC) has been studied to identify how the fresh and hardened properties of SCC are affected by the addition of fibre. The basalt fibres of 3, 6, 12 and 24 mm in length are incorporated into the SCC mixtures as 0%, 0.1%, 0.3% and 0.5% of concrete volume. After the progression of flow diameter, T 500 flow time and V-funnel time tests on the fresh SCC, the tests of compressive strength, flexural strength, splitting tensile strength, rapid chloride permeability and water penetration have been conducted to identify the hardened properties of SCC produced with basalt fibre. The response surface method is employed in the conducted multi objective optimization analysis considering the maximisation of the compressive, flexural and splitting tensile strength parameters while minimising the response criterion of rapid chloride permeability and water penetration depth. The results reveal that the use of basalt fibre decreases the workability but improves the mechanical properties of SCC. The highest flexural and splitting tensile strength results are obtained from the concrete mixtures incorporated with the content of 0.5% fibre having the length of 24 mm. Whereas, the highest compressive strength result is obtained from the mixtures containing the fibre content of 0.1% for the utilised fibre lengths of 12 mm and 24 mm. The optimum volume fraction and length of basalt fibre are determined as 0.49% and 21.12 mm considering the optimized strength and permeability based durability properties of SCC. [ABSTRACT FROM AUTHOR]

Highlights • A study about the performances of FR concretes is presented. • Both flexural and tensile strengths are investigated. • The experimental program encompasses straight and hooked steel fibers. • The effect of fiber dosage has been assessed in detail. • The critical dosage of fibers to ensure hardening behavior is assessed. Abstract High Performance Fibre-Reinforced-Cement-Composites and Ultra-High Performance Fibre-Reinforced-Concretes, also named HPFRCCs and UHPFRCs respectively, are today widely used as repair and strengthening existing structures, such as bridge decks, pavements, piers etc. Simple test methods to characterize its mechanical behavior are requested, in order to ensure that the product meets the designer’s requirements, especially in term of tensile behavior. Various test methods are available, even though a proper correlation between direct and indirect tensile (e.g. flexural) tests is needed. In this paper a model based on the “Composite Material Theory” (CMT) was developed to predict the flexural behavior of three commercialized SFRCs once the direct tensile strength is measured. A good agreement was found between experimental results and the values predicted by the model. [ABSTRACT FROM AUTHOR]

Highlights • The differences between natural and artificial hydraulic lime mortars were revealed. • NHL mortar have preferable fluidity compared to the artificial lime mortars. • The mechanical properties of artificial lime mortar have advantages over NHL mortar. • A part of artificial lime mortars is nearby to NHL mortar in environmental resistance. • Three kinds of lime mortars have big difference in hydration and carbonation reaction. Abstract To evaluate the differences of properties between natural and artificial hydraulic lime mortars, the macro and micro properties of natural hydraulic lime (NHL2 and NHL5) mortars, white Portland cement-aerial lime-based (CL15 and CL25) mortars and slag-aerial lime-based (SL20 and SL40) mortars were studied through the examination of their physical and mechanical properties, environmental resistance properties, hardening mechanism and microstructure of lime mortars or pastes. The results show that the NHL mortars have preferable fluidity compared to the artificial CL and SL mortars, while the mechanical properties of artificial CL and SL mortars are advantageous compared to those of NHL mortar. In terms of environmental resistance, the water resistance of SL mortar is best, closely followed by the CL mortar, and the NHL mortar is relatively weak; moreover, CL mortar shows the best sulphate resistance, and SL mortar has the best alkali resistance. The hydration reaction (or pozzolanic reaction) and carbonization reaction could occur in the three kinds of hydraulic lime pastes, and the hydration reaction of the NHL and CL pastes mainly occur in the early stage of paste hardening (before 28 days), while the pozzolanic reaction of the SL paste reach a high degree at early hardening stage (28 days) and still maintains a certain reaction rate in the later period. The carbonation reaction process of the three kinds of lime pastes continues to the later period of the hardening, and the carbonation rate of SL pastes in the later stage would be obviously enhanced; furthermore, the carbonation degree of NHL paste is obviously higher than that of the CL and SL pastes. The different hydration-hardening process and mechanism of the three lime pastes lead to differences in the morphology and pore structure among them. There are more large-size pores in NHL5 paste (the pore volume in the range of pore diameter greater than 200 nm reaches 63.13%), while the pore size of the SL paste is relatively small (the pore volume in the range of pore diameter less than 100 nm reaches 44.15%). The porosity during the 180 days curing period was as follows: SL40 (27.32%) < CL25 (29.65%) < NHL5 (33.09%). [ABSTRACT FROM AUTHOR]

Fiber distribution is an important factor which affects the fresh and hardened properties of composites. A variety of methods are available for studying the fiber distribution but image analysis is more widely used for fiber reinforced cement-based composites (FRCs). In this paper, different fiber distribution methods are discussed in detail including optical microscope, scanning electron microscopy, fluorescence microscopy and X-ray computed tomography. It is found that fluorescence microscopy is more widely used for studying fiber dispersion in FRCs and can be applicable to the synthetic fibers. [ABSTRACT FROM AUTHOR]

The buckling capacity of uniformly compressed flat plates has been investigated in this study. Material properties were characterized based on parameterization of the stress-strain curves using a simple and novel mathematical expression. Idealized stress-strain relationships were developed using the proposed material model and extensive parametric numerical analyses were conducted to investigate the effect of the material stress-strain properties on the buckling capacity of flat plates. For stress-strain curves with a yield plateau, the results of the parametric study showed a minimal influence of the material properties on the buckling capacity of the plates whereas a significant effect of the strain-hardening properties was observed in plates with round-house curves. Ultimately, the proposed stress-strain model was shown to be remarkably useful for capturing the relevant intricacies associated with material nonlinearity when predicting the buckling capacity and post-buckling behavior of uniformly-compressed flat plates. [ABSTRACT FROM AUTHOR]

This study is motivated by increasingly prevalent use of cable-tensioned spatial steel structures and suspension bridges. Fire is one of the extreme conditions that need to be taken into consideration in the design of such structures. In this paper, steady-state tests have been conducted on steel cables with tensile strength of 1860 MPa, which consist of a group of 7-wire twisted strands, to study their full range of stress strain relationships at elevated temperature. Thermal elongation test of steel cables has also been conducted. A charge-coupled device camera (CCDC) system is used to capture the full range of stress-strain relationship of high tensile strength steel cables till rapture at elevated temperature. The reduction factors of proportional limit, elastic modules, effective yield strength and rupture strength at different temperature were obtained from the steady state tests and compared with that proposed by EN 1992-1-2. The experimental work discovered that EN 1992-1-2 overestimated effective strain up to 2% and ignored the stress-hardening phase for high tensile strength cables within the full temperature range. The effective yield strength with 1.25% strain and a full range of stress-stain model considering stress-hardening phase are proposed. Finally, several sets of reduction factors and thermal elongation coefficient as a function of temperature have been proposed by fitting the test results. The reduction factors of pre-stressing strands proposed by EN 1992-1-2 for pre-stressing concrete is found not suitable for steel cables which are widely used for pre-tensioned steel structures. The reduction factors proposed in the present paper are found to be reasonable for steel cables. The experimental work also shows that the mechanical properties of steel cables at elevated temperature depends on whether the cable is made from straight wires or twisted wires. [ABSTRACT FROM AUTHOR]

The bond behavior of epoxy-coated rebar embedded in two different ultra-high performance concrete (UHPC) mixtures is experimentally investigated by a uniaxial pullout test, and the effect of embedment length, side cover, and mixture type on the bond stress-slip relationship is predicted using a double-phase analytical model. The bond mechanism and failure modes of rebar in UHPC are similar to those observed in normal concrete. The embedment length and side cover have significant influence on the bond behavior of epoxy-coated rebar in UHPC, and more drastic bond stress hardening and softening are observed for the case of larger embedment length and side cover. Two UHPC mixtures exhibit comparable bond strength and critical development length because they have close mechanical properties gained at test age. The adopted analytical model matches well with the experimental bond-slip response of epoxy-coated rebar in UHPC, and both the characteristic parameters in the model show an increasing trend when more dramatic hardening and softening of bond stress exhibit. [ABSTRACT FROM AUTHOR]

The coupling action of calcium leaching and chloride attack is an important durability problem for the cement-based materials served in long-termly in the environmental water like seawater or groundwater containing chloride. This paper investigates the influence of calcium leaching on the chloride diffusivity in cement-based materials by the corrosion experiment, in which the hardened cement paste (HCP) specimens are immersed into three corrosion solutions with the same chloride concentration, such as 1 M sodium chloride solution, 1 M ammonium chloride solution and the mixed solution of 1 M sodium chloride and 3 M ammonium nitrate. Some measurements, like the phenolphthalein, saturation-drying weighing, mercury intrusion porosimetry (MIP), Scanning Electron Microscopy (SEM/EDS), X-ray diffraction analysis (XRD) and rapid chloride test (RCT), are used to analyze the leaching behaviors and its influence on the chloride diffusivity of HCP, characterized by leaching depth, pore structure, morphology, calcium-silicon ratio, chloride-silicon ratio, phase composition and free chloride ion content. Results show that, in the calcium leaching process, the compactness, calcium hydroxide content and calcium-silicon ratio of C-S-H gel of HCP decreases with the leaching time. The calcium leaching causes the reduction of the physically chloride-bound ability and the chemically chloride-absorbed ability in HCP, and it results in high chloride diffusivity. [ABSTRACT FROM AUTHOR]

The modification in lime mortar to preserve the historic structures is the growing trend in current scenario. The natural polymer, areca nut extract in concentrations of 3% and 5% was incorporated in the lime mortar to modify the fresh and hardened state properties. The microstructural analyses of the modified mortar were studied by X-ray powder diffraction, FTIR spectroscopy, SEM−EDS analysis. The results obtained from these analytical techniques are substantiated with the results of TG-DTA. Inclusion of areca nut extract in the lime mortar proves to be superior against the conventional mortar in mechanical, physical and durability properties. [ABSTRACT FROM AUTHOR]

In this study, the effects of different amount of dosages (250, 300, 350 and 400) on the electrical cure of hardening (setting) concrete have been investigated. In experiments, 10 cm × 10 cm × 35 cm moulds have been used. Different combinations of stress intensity (0 V, 40 V, 60 V, 80 V and 100 V) have been used on mixtures for 24 h by AC power-supply. The measurements have been done at room temperature. Electrical cure and hydration time of the specimens with electric current application have been investigated. Through the application of 100 V stress intensity to the 250, 300, 350 and 400 dosage concretes, their final setting time are shortened 510, 380, 410 and 500 min, respectively when they are compared to the same dosage reference concretes. Scanning Electron Microscope (SEM) views have been investigated from 300 dosage concretes and It is determined that hydration reactions accelerate as stress intensity increases (from 0 V to 100 V). It has been concluded that hydration time can be shortened both as a result of applying electrical current to concrete and increasing the amount of dosage of concrete (from 250 to 400). [ABSTRACT FROM AUTHOR]

The effects of fly ash and slag on fresh and hardened properties of self-compacting concrete (SCC) were investigated using four CEM I 52.5 N cements produced at different factories according to ASTM C150 , two polycarboxylate-acid based superplasticisers, two class F fly ashes and one slag. The differences in the cement characteristics were enough to affect the SCC flow properties. The compatibility of cement and admixtures depended mostly on the concentration of C 3 A, C 2 S/C 3 S ratio, the specific surface area of the cement and the type of superplasticiser used. A protocol to assess the sensitivity of a SCC mix design to a type of cement is proposed. [ABSTRACT FROM AUTHOR]

The present research investigates the performance of mortar prepared with high-volume ground glass fiber (GGF) incorporated as partial replacement of Portland cement. Several binary and ternary mixtures with up to 50% cement substitution were investigated to evaluate rheological properties, heat of hydration, strength development, drying shrinkage, electrical resistivity, and carbonation. The incorporation of up to 50% GGF was found to reduce yield stress by up to 50% compared to control mortar without any GGF. On the other hand, this resulted in up to 100% increase of plastic viscosity of mortar in comparison with the Reference mortar cast with 100% Portland cement. The rate of structural build-up at rest of the tested mortars, that reflects the thixotropic nature of the mortar, decreased from 7.1 to 0.8 Pa/min with cement substitution by 50% of GGF. Reduction in 91-day compressive strength from 34 to 28 MPa was observed with 50% cement substitution by GGF. The coefficient of pozzolanic activity of mortar cast with 10% to 50% GGF ranged from 0.18 to 0.71 at 91 days, compared to mixtures containing 50% cement substitution with Class F fly ash (FA-F), Class C fly ash (FA-C), or blast furnace slag (SL) where the 91-day coefficient of pozzolanic activities were 1.80, 1.46, and 1.21, respectively. The incorporation of 10% to 50% GGF reduced the 91-day drying shrinkage by 0–20%. At 50% GGF replacement, the electrical resistivity was enhanced from 10 to 88 kΩ.cm at 91 days, while the carbonation coefficient increased by about 100%. The incorporation of 15% or 25% GGF in ternary systems containing either FA-C, FA-F, or SL was effective in enhancing compressive strength, with values ranging between 34 and 49 MPa. The best performance was observed in the case of the GGF/FA-C ternary binders, followed by the GGF/SL, and GGF/FA-F systems where 91-day compressive strength gains of up to 45%, 28%, and 10%, respectively, were observed compared to the Reference mixture with 100% Portland cement. [ABSTRACT FROM AUTHOR]

Hereby paper presents the results of the research on determining the impact of cement and aggregate type on the formation of hardening temperature and mechanical properties of concrete. In the study, the six cement types, which contain up to 70% of main non-clinker constituents and four types of aggregate (basalt, granite, limestone and gravel) were used. The test results showed that cements with low clinker content allow to significantly reduce hardening temperature of concrete and thus, minimize the risk of cracks formation in concrete. Aggregate type has not affected concrete hardening temperature. However, it has an impact on magnitude of generated thermal stresses, caused by different thermal expansion coefficients of the aggregates. The most favourable aggregate types to use in mass concrete from the all analysed are granite, basalt and limestone. Usage of gravel aggregate in concrete, consisting mainly of quartz, might lead in certain unfavourable conditions to crack formation, caused by generated thermal stresses. [ABSTRACT FROM AUTHOR]

This study focused on the performance of hardener-free epoxy-modified mortar (HFEMM) with pyrolysis tar (PT), a by-product of the green wood industry. HFEMMs were prepared with amounts of 1, 3, and 5% epoxy resin. For the HFEMM with a 1% epoxy resin mixing rate, 5, 10, 15, and 20% of the epoxy resin were replaced with PT. The highest hardening rate was observed for the HFEMM with 1% epoxy resin, whereas the amounts of hardened and unhardened epoxy resin were the largest at 5%. When 1% epoxy resin was replaced with PT, the hardening rate increased to 10%. When 10% PT was substituted with 1% epoxy resin, the compressive, flexural, and adhesive strengths increased because of the higher hardening rate. X-ray diffraction result showed that an increase in the epoxy resin content and the PT replacement rates resulted in lower amounts of calcium hydroxide and lower semi-adiabatic and maximum exothermic temperatures. These results showed that the use of PT in the HFEMM could improve its performance while providing an avenue to recycle PT. [ABSTRACT FROM AUTHOR]

An experimental investigation was undertaken on the physical characterization of a flax fiber-reinforced concrete (FFRC) in both fresh and hardened state. The objective of this study is to provide guidance for the mix-design of these FFRC. The study was conducted from two points of views: improving the workability of the concrete in a fresh state and improving the flexural strength in the hardened state. Several parameters have been studied independently as fiber length, fiber content, or the paste content. The characterization of flax fibers highlighted a high water absorption capacity which must be taken into account for the concrete mix-design. In addition, the flax fibers significantly impact the compactness of granular skeleton. For the characterization of concrete, testing in the fresh state showed a significant decrease of the workability of concrete with the addition of flax fibers. However, the use of shorter fibers, allows to reduce this damaging influence on the fresh concrete workability. Moreover, increasing the paste content allows compensating this fluidity loss. In the hardened state, the increase of the fiber content enhances the flexural strength, but a decrease of the compressive strength is observed. A greater porosity of the concrete was also observed with the incorporation of flax fibers. An increase in porosity was also observed when increasing the paste content. [ABSTRACT FROM AUTHOR]

The homogeneous state of the concrete in the fresh state has consequences on their properties in the hardened state. The use of pozzolanic concrete must be carefully evaluated, because the physical and chemical differences of each pozzolan have consequences on concrete hardened state properties. In this work, two physical and chemically different pozzolans were used to evaluate the effect on concrete microstructure and its basic hardened state properties. Scanning electron microscopy (SEM) was used and can be an effective tool in the analysis of the microstructure allowing a better understanding of the properties of concrete in hardened state. It allows showing that the differences in the two pozzolans (metakaolin and diatomite) promote different microstructures as well as different final properties of pozzolanic concrete. Moreover, it was also shown that the use of a water reducing agent, to adjust workability instead of water, promotes an improvement in both the microstructure and the hardened state features such as porosity and mechanical strength. [ABSTRACT FROM AUTHOR]

Contact-hardening is a new type of binding property for amorphous calcium silicate hydrate (C-S-H) with which a hardened specimen can be prepared in a few minutes by compressing C-S-H powders directly. However, the relation between contact-hardening behaviours and the drying conditions of powders is still poorly understood. In this study, the influence of air-drying and oven-drying on the physical properties and microstructure of hydrothermally synthesised C-S-H powders were investigated. The results provide further insight into the contact-hardening behaviours of these powders by measuring the bulk density, mechanical strength and water-resistant properties of the compacts. Factors affecting particle-particle contact and hardening of C-S-H powders are discussed in parallel with the mechanical properties and microstructure of the compacts. The result highlights that the moisture content, which is highly related to the drying conditions, is essential to contact hardening of C-S-H. [ABSTRACT FROM AUTHOR]

In this work, sulfonated asphalt was chosen as an admixture, and the influence of the quantity (1%, 2%, 3%, 4% of the weight of the cement) of sulfonated asphalt on the mechanical properties of hardened cement slurry was studied. Moreover, the micro-morphology and porous structure characteristics were examined using the SEM and nitrogen adsorption-desorption method, respectively. Studies showed that the addition of asphalt had great potential to improve the tensile strength and toughness of cement paste. The tensile strength of cement paste with 3% sulfonated asphalt increased by 45% at 7 days and 17% at 28 days in comparison with that of specimens without sulfonated asphalt. In addition, 2–3% sulfonated asphalt levels were advantageous for improving the toughness of oil well cement paste. Asphalt particles caused crack bending and deflection as well as toughened oil well cement paste. The addition of 3% asphalt had a positive good effect on the pore size distribution in cement paste. The addition of asphalt decreased the compressive and flexural strength of cement paste at the same curing age. The content of 4% asphalt increased the pore size and caused deterioration of the mechanical properties of cement paste. It is necessary to balance the mechanical properties of cement paste and the amount of asphalt in the range 2–3% to be beneficial for this application. [ABSTRACT FROM AUTHOR]

The aim of this research is supporting the recycling of ladle furnace slag from steel making industry. Ladle furnace slag is generally treated as a waste because of its volume instability with free-CaO and free-MgO crystalized during the slow cooling process. Regarding this by-product, from the previous research, rapid cooling technique with high pressured air was introduced, and rapid hardening properties of rapidly cooled ladle furnace slag (RCLFS) was introduced. In spite of outstanding rapid hardening performance, because of hydrogarnet, the main hydration product of main component for rapid reaction, RCLFS has low compressive strength and severe shrinkage as the drawbacks. In this research, to resolve these drawbacks, gypsum was incorporated and induced formation of ettringite. By using modified Bogue equation, the required appropriate amount of gypsum was determined as 37% of RCLFS weight, and a series of experiments were conducted to prove it. From the results of the experiment, when the RCLFS contained gypsum, ettringite was generated and due to the ettringite, compressive strength was continuously increased with decreased porosity. This result is expected to contribute to recycle the RCLFS as a rapid hardening material with more stable performances. [ABSTRACT FROM AUTHOR]

Organic surface treatment agents, such as silanes, have been widely used for the improvement of the surface quality of cement-based materials, but their lower weather resistivity compared to the inorganic treatment agents is the main shortage. The tetraethyl orthosilicate (TEOS) silane was used for the surface treatment of hardened cement-based material by utilizing the inorganic in-situ hydrolysis product of SiO 2 . Effects and mechanisms of TEOS for surface treatment of hardened cement-based materials were investigated with a comparison study of the normally used inorganic concrete sealer sodium silicate, i.e., the water glass, and the water repellent methyltriethoxysilane (MT-silane). Compressive strength and mass transport property (water absorption rate or water vapor transport property) investigations suggested that the reported benefits of TEOS on hardened cementitious materials will not occur when it was applied onto the relatively young cement-based materials, and the properties could be worse than the sodium silicate- and MT-silane-treated samples, and the negative effect of TEOS on the hydration of cement at early age could be the reason as revealed by the hydration heat calorimetry tests. For the old cementitious material, the blocking of pores by the in-situ hydrolysis and condensation of TEOS, forming silica sol/gel, as well as its quick (comparable to that of sodium silicate) pozzolanic reaction with calcium hydroxide, forming additional calcium silicate hydrate, contribute to the improved surface quality. IR spectroscopic investigation showed that MT-silane react with calcium hydroxide, but in a slower rate than that of TEOS and sodium silicate, and no C-S-H gel can be formed, thus no densification of the structure could be resulted when using MT-silane. [ABSTRACT FROM AUTHOR]

High-porosity cement foams based on ternary blends of Portland cement, metakaolin and silica fume were prepared by the pre-foaming method. The effects of ternary blends on the early-age properties, air-void structure and hardened state properties of cement foams were investigated. The effect of metakaolin and silica fume on stabilizing air-voids was observed, and the collapse of cement foams during the hardening process was avoided by addition of metakaolin. Moreover, the compressive strength of the prepared 91% high-porosity cement foams was enhanced by addition of metakaolin and silica fume. The compressive strength and thermal conductivity reached 0.74 MPa and 0.054 W/m K, respectively. However, metakaolin and silica fume had a negative impact on the workability of the cement foam. [ABSTRACT FROM AUTHOR]

Mixing procedure as well as type of mixing highly influence the fresh and hardened properties of self-compacting concrete (SCC) besides other parameters such as mix proportions, water to powder ratio, and mineral and chemical admixtures. This study attempts to investigate the effect of different types of mixing on the properties of SCC for providing a guideline in choosing the appropriate mixer type. Further, the influence of time of addition of superplasticizer on the properties of concrete is also studied. Four different types of mixer such as pan, Eirich, drum, and ribbon mixers are employed. It is found that the compressive strength and horizontal slump of mix obtained through Eirich mixer is higher compared to all other mixes. Further, no significant influence of time of addition of superplasticizer is noticed on hardened properties whereas marginal increase in flow is observed with delayed addition. [ABSTRACT FROM AUTHOR]

Fly ash is a principal by-product of the coal-fired power plants and is well accepted as a pozzolanic material that may be used as a mineral admixture in concrete. High-volume fly ash (HVFA) concrete, which has typically 50–60% fly ash as the total cementitious materials’ content, is widely used to achieve the sustainable development of concrete industry. Compressive strength development is the most important engineering property of hardening concrete. This paper presents a numerical procedure to evaluate the compressive strength development of HVFA concrete. The numerical procedure starts with a blended hydration model considering cement hydration, fly ash reaction, and interactions between cement hydration and fly ash reaction. Using the hydration model, the hydration degree of cement and reaction degree of fly ash are determined as functions of curing age. Furthermore, calcium silicate hydrate (CSH) contents of hardening HVFA concrete are calculated using reaction degrees of binders and mixing proportions of concrete. Finally, the compressive strengths of hardening HVFA concrete are determined using CSH contents. The proposed numerical procedure is valid for concrete with different water to binder ratios (ordinary strength concrete and ultra high strength concrete) and different fly ash contents (low volume fly ash and high volume fly ash). [ABSTRACT FROM AUTHOR]

Lightweight aggregate (LWA) can provide internal curing to lightweight aggregate concrete (LWAC) due to the water absorption and desorption capability of ceramsite. Hence, the addition of ceramsite has a strong effect on the early age autogenous shrinkage of LWAC. In this paper, the early-age autogenous shrinkage of LWAC with different prewetting degree LWA was quantitatively studied when the same net water to cement ratio (NWC) or total water to cement ratio (TWC) was used. During the liquid phase and skeleton-formational phase, the positive effect of the 24 h prewetted ceramsite on the early-age autogeneous shrinkage of LWAC is obvious. During the hardening phase, the LWACs show small expansion strains. Therefore the early age autogeneous shrinkage of LWAC decreases with the increase of prewetting degree of ceramsite for the same NWC or TWC. [ABSTRACT FROM AUTHOR]

The influences of partially replacing cement with ground clay-brick on properties of fresh and hardened concrete were investigated. In this study, three different replacement levels (10%, 20%, and 30%) and three types of clay-brick-powder (CBP) with different particle sizes (Type A, B, and C) were adopted. The test results show that CBP reduced the slump of fresh concrete significantly as the replacement level was over 10%. All concrete specimens had similar density around 2400–2500 kg/m 3 . As the replacement level increased, the early age strength decreased. However, as the curing age increased, strength of concrete with CBP was similar to that of reference concrete. Most concrete containing CBP had 90-day compressive strength over 50 MPa, 28-day flexural strength in the range of 10–12 MPa, and 28-day splitting tensile strength of 2–4 MPa. Static elastic modulus was between 15 and 30 GPa. The specimens had low chloride ion penetrability with total passed charge value was less than 1742 C. After 300 freezing–thawing cycles, the strength deduction and mass loss were less than 16% and 1.6%, respectively. The water absorption increased with the replacement level, while the autogenous shrinkage can be reduced significantly as over 10% of cement replaced by CBP. The non-evaporable water decreased but not proportionally to the substitution level. [ABSTRACT FROM AUTHOR]

In this study, four types of pozzolanic cements—CEM II/A-P, CEM II/B-M, CEM II/B-P and CEM IV/B-M, together with CEM I, were used to produce self-compacting concretes. However, it was not possible to obtain self-compacting properties with CEM II/B-P and CEM IV/B-M. The fresh concrete properties and the hardened concrete properties—sorptivity, water penetration under pressure, carbonation and rapid chloride penetration—were determined on the concretes stored in air for 3 years. Drying shrinkage was monitored for up to 4 months, and compressive strengths were measured at the age of 28 days after a standard water curing. [ABSTRACT FROM AUTHOR]

This paper presents deflection hardening behaviour of jute strands reinforced lightweight cementitious composite under flexural loading. The effects of volume fractions of jute strands and the amount of lightweight fine aggregate (LWFA) as partial replacement of natural fine aggregate (NFA) on the deflection hardening and multiple cracking behaviour are also evaluated in this study. Five different types of mortars containing 0%, 50%, 75%, 100% and 150% (by wt.) light weight fine aggregates are produced. Jute strands reinforced cement composites containing four different volume fractions of jute strands of 2%, 4%, 6% and 8% are prepared using each type of light weight mortar. The specimens were tested in third-point loading and the results show deflection hardening with multiple cracking of jute strand reinforced lightweight cement composites. The composites also show high toughness and toughness indices values, indicating the potential of this environmental friendly highly ductile composite in building and construction applications. [ABSTRACT FROM AUTHOR]

This study investigated two artificial materials—biomass fly ash (AFA) and a new synthesized composite from clay and silica gel waste (CSG)—as additives for Portland cement. AFA has very weak pozzolanic properties and acts as an inert microfiller, whereas CSG is a pozzolana. It was determined that up to 15 wt.% of ordinary Portland cement (OPC) can be replaced with either additive without impairing the strength properties of the samples. The positive effect of AFA additive on the strength properties of OPC is associated with significant acceleration of the calcium silicate hydration process, whereas this effect for the CSG additive is related to the formation of stratlingite (C 2 ASH 8 ), hydrogarnet (C 3 AS x H 6-2 x ), and an additional amount of calcium silicate hydrates. [ABSTRACT FROM AUTHOR]