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The standard codes of practice on the rammed-earth construction are limited. It is essential to ascertain the characteristic compressive strength of the cement-stabilized rammed earth (CSRE) for the structural design of CSRE walls. The test procedures for determining the characteristic compressive strength of CSRE are not available in the standard codes of practices. The specimen size and its slenderness can affect the compressive strength of CSRE elements. This paper deals with the relationships between the specimen's aspect ratio and compressive strength for CSRE using two cement contents (7 and 10%) and two densities. Both cylindrical and wallette specimens having an aspect ratio varying between 2 and 5.81 were tested for compressive strength. The results show that there is hardly any reduction in compressive strength as the aspect ratio was increased from 2 to 5.81 (a reduction in compressive strength of 1 and 3-5% for specimens with density of 1,800 and 1,700 kg=m³, respectively). The study clearly demonstrates that the characteristic compressive strength of CSRE can be obtained by testing cylindrical (150 mm diameter and 300 mm height) or prism specimens (150 mm square cross section and 300 mm height) without applying any correction factor. Furthermore, since the moisture content in the specimen has a significant influence on the compressive strength of CSRE, it is recommended to adopt the wet compressive strength for structural design. [ABSTRACT FROM AUTHOR]

Samples of piezoelectric cement, consisting of equal volumes of lead zirconate titanate and type I Portland cement, were treated through a heating technique and cured for controlled lengths of time to produce notable piezoelectric properties. Piezoelectric properties were measured by considering curing times of 1, 3, and 7 days, and applying 23 °C or 140 °C treatments on the piezoelectric cement samples. Curing time showed minor effects on the piezoelectric strain factor d 33 , relative dielectric constant ε r , and electromechanical coupling coefficient K t at late ages for specimens that were cured for more than 3 days. Pretreatment with higher temperatures on piezoelectric cement is expected to obtain higher d 33 and ε r values than posttreatment would obtain. Two heat treatments at 140 °C and 1 day of curing for piezoelectric cement provide superior d 33 and ε r values, with d 33 = 110.9 pC/N and ε r = 756 at 100 days. However, it is necessary to enhance the K t of piezoelectric cement at least 3 days’ curing. [ABSTRACT FROM AUTHOR]

Cattle manure ash (CMA) is an industrial waste produced from the combustion of cattle manure. This research examined the effect of added CMA produced at combustion temperatures of 500 °C, 650 °C and 800 °C on the workability and mechanical properties of magnesium phosphate cement (MPC). The obtained data indicates that CMA decreases workability and mechanical properties of MPC to which it is added. However, relatively higher combustion temperature in CMA preparation can diminish the adverse effect that CMA exerted on mechanical properties and workability of MPC. CMA promotes the formation of struvite in the hydration reaction of MPC. [ABSTRACT FROM AUTHOR]

An experimental research was conducted with the objectives to study the effects silanes (amino, vinyl, and epoxy-based) and their derivatives (silane oligomers and silane nanoparticles) on cement hydration and mechanical properties of mortars. Silanes and silane derivatives are used as coupling agents to combine different compositions in mortars and to chemically react with calcium silicate hydrates to introduce organic component into C S H structure. The use of silanes retarded the cement hydration. However, silane derivatives were found to effectively mitigate the retardation. Liquid-state 29 Si nuclear magnetic resonance (NMR) spectroscopy indicated that silanes and silane derivatives have different hydrolysis and condensation products in the solutions of cement pastes. Further analysis of silicon concentration in the solution indicated that the hydrolysis and condensation products of silane oligomer is opt to be in the solution, instead of adsorption onto the surface of cement hydration products, to retard the cement hydration. Ordinary mortars with the silanes and silane derivatives showed general enhancement in flexural strength and some improvement in compressive strength after curing for 7 days and 28 days. Due to good strength properties, negligible hydration retardation, and simple preparation method, epoxy-based silane oligomer was selected for further study in high-strength mortar. Results indicated that the compressive strength, splitting tensile strength, and elastic modulus of the high-strength mortar were increased by 20%, 38%, and 13%, respectively, compared with the control mortar. [ABSTRACT FROM AUTHOR]

This paper is aiming at evaluating the possibility of polycarboxylate-based material used as grinding aid for cement production and studying its influence on cement properties under laboratory condition. Results indicated that polycarboxylate grinding aid (PC-GA) obtained by free radical polymerization can provide almost the same grinding efficiency as Triethanolamine (TEA). Besides, PC-GA can also optimize the particle size distribution and unify the particle size. The SEM result revealed that the effective was attributed to the function that PC-GA reduced the amount of absorbed fine particles on cement thus increased the compact force. What’s more, the employment of PC-GA during grinding process increased the fluidity of cement paste significantly while did no obvious harm to other properties of cement. [ABSTRACT FROM AUTHOR]

Earthen building materials bear interesting environmental advantages and are the most appropriate to conserve historical earth constructions. To improve mechanical properties, these materials are often stabilized with cement or lime, but the impact of the stabilizers on the water transport properties, which are also critical, has been very rarely evaluated. The researchers have tested four earth-based repair mortars applied on three distinct and representative rammed earth surfaces. Three mortars are based on earth collected from rammed earth buildings in south of Portugal and the fourth mortar is based on a commercial clayish earth. The main objective of the work was over the commercial earth mortar, applied stabilized and not stabilized on the three rammed earth surfaces to repair, to assess the influence of the stabilizers. The other three earth mortars (not stabilized) were applied on each type of rammed earth, representing the repair only made with local materials. The four unstabilized earth materials depicted nonlinear dependence on t1/2 during capillary suction. This behavior was probably caused by clay swelling. Stabilization with any of the four tested binders enabled the linear dependence of t1/2 expected from Washburn's equation, probably because the swelling did not take place in this case. However, the stabilizers also significantly increased the capillary suction and the capillary porosity of the materials. This means that, in addition to increasing the carbon footprint, stabilizers, like cement and lime, have functional disadvantages that discourage their use in repair mortars for raw earth construction. [ABSTRACT FROM AUTHOR]

The use of recycled construction and demolition (C&D) materials in unbound and cement stabilized pavement base/subbase applications has generated growing interest in recent years. C&D materials consisting of crushed brick (CB), recycled crushed aggregate (RCA), and reclaimed asphalt pavement (RAP) have been investigated in unbound and cement stabilized pavement base/subbase applications. However, the high carbon footprint of using cement for pavement base/subbase stabilization has led to this research to seek alternative low-carbon binders. This study evaluates the behavior of C&D materials when stabilized with geopolymers. Fly ash (FA) and ground granulated blast furnace slag (S) were used as pozzolanic binders and a different alkaline activator solution to pozzolanic binder ratio was tested. A maximum of 4% of dry weight of soil was used for geopolymer stabilization of the C&D materials. The binders used were either 4% FA, 2% FA+ 2% S, or 4% S. The geotechnical engineering and strength properties of these geopolymer-stabilized C&D materials were evaluated to ascertain their performance for pavement base/subbase applications. Elastic modulus, compressive strength, and resilient modulus of the blends were tested and analyzed in this research. Both the resilient modulus of the C&D materials and compressive strength were found to increase as a result of geopolymer stabilization. Geopolymer stabilization was found to be most effective for RCA. Higher compressive strength will be achieved by slag-based geopolymer stabilization when compared with fly ash--based geopolymer stabilization. The effect of alkaline activator to pozzolanic binder ratio on the enhancement of geotechnical properties of C&D materials was also analyzed. The performance of the geopolymer-stabilized C&D materials was furthermore compared with that of traditional cement-stabilized C&D materials. Geopolymer-stabilized RCA and RAP were found to be a viable and sustainable option for the stabilization of future pavement bases/subbases. [ABSTRACT FROM AUTHOR]

Compressed earth blocks, a form of earthen construction, is a growing field of natural building. It is a low-cost, locally available material that provides high thermal capacity with low environmental impact. Earthen blocks have been primarily used in warmer climates; however, there is increasing interest in using the blocks in cold climates. Limited research has been done on long-term durability in cold climates. In this study, combinations of cement and lime stabilizers were tested with metakaolin and Plasticure, a water repellant, to determine freeze-thaw durability. Blocks were exposed to up to twelve 48-hour freeze-thaw cycles. Prisms were tested in compression to failure in both the wet and dry condition as a measure of deterioration. Freeze-thaw damage occurred when water was readily available via capillary action. Blocks with 7.5% cement content provided optimum strength retention; however, 10% cement provided higher strengths. The addition of lime, metakaolin, and Plasticure to a 5% cement-stabilized block increased dry strength retention by 75 to 146%, but there was no significant difference when wet. Plasticure reduced variability in strength reduction from as high as 91 to 24%, and increased strength retention by up to 75%. Reductions in both strength and water strength coefficients were observed in different combinations. [ABSTRACT FROM AUTHOR]

The portfolio of available synchrotron radiation techniques is increasing notably for cements and pastes. Furthermore, sometimes the terminology is confusing and an overall picture highlighting similarities and differences of related techniques was lacking. Therefore, the main objective of this work is to review recent advances in synchrotron techniques providing a comprehensive overview. This work is not intended to gather all publications in cement chemistry but to give a unified picture through selected examples. Crystallographic techniques are used for structure determination, quantitative phase analyses and microstructure characterization. These studies are not only carried out in standard conditions but synchrotron techniques are especially suited to non-ambient conditions: high temperatures and pressures, hydration, etc., and combinations. Related crystallographic techniques, like Pair Distribution Function, are being used for the analysis of ill-crystalline phase(s). Furthermore, crystallographic tools are also employed in imaging techniques including scanning diffraction microscopy and tomography and coherent diffraction imaging. Other synchrotron techniques are also reviewed including X-rays absorption spectroscopy for local structure and speciation characterizations; small angle X-ray scattering for microstructure analysis and several imaging techniques for microstructure quantification: full-field soft and hard X-ray nano-tomographies; scanning infrared spectro-microscopy; scanning transmission and fluorescence X-ray tomographies. Finally, a personal outlook is provided. [ABSTRACT FROM PUBLISHER]

Cemented gangue backfill (CGB, a mixture of coal gangue, cement and water) is widely used in China for backfilling in coal mines. The addition of fly ash to CGB mixtures can help them to have favourable environmental and economic performance. In addition, mechanical stability and durability are also important performance criteria for CGB, and these two criteria are closely related to the suction of CGB. The evolution of suction in CGB is influenced by binder hydration, which is an exothermic process affecting the variation in temperature of CGB. To examine the coupled effects of binder hydration and temperature (including the temperatures of a CGB mixture and its surroundings), in this study a numerical model was developed to predict the development of suction in a CGB mixture containing fly ash. Data from a laboratory study were used to validate the developed model, and it was found that the results of the model simulation and the experimental study were in good agreement. Therefore, the proposed model was applied to simulate and determine the development of suction within the CGB mixture over curing time. The results obtained can contribute to better design and preparation of CGB mixtures, as well as better prediction of the evolution of suction within CGB structures. [ABSTRACT FROM AUTHOR]

A two-phase experimental study on the effect of simultaneous partial replacement of cement and fine aggregate with fly ash on the mechanical and time-dependent properties of high-volume fly ash concrete (HVFAC) is presented. The results of the first phase of the study show that it is possible to make structural grade HVFAC with 50% of cement and an additional 30% of fine aggregate replacement that has a similar compressive strength to that of the control cement concrete and with adequate workability. In the second phase of the study the mechanical and time-dependent properties of HVFAC with a mass of fly ash of 50-70% of the total mass of cementitious materials were tested. The results show that with the increase in fly ash content the compressive strength of HVFAC increased by 22% on average at all ages tested. With the exception of the early-age compressive strength, it was found that the European standard EN 1992-1-1:2004 provisions for ordinary cement concrete underestimate the mechanical properties and significantly overestimate the shrinkage and creep of HVFAC. Better correlation with experimental results was obtained using different coefficients developed for HVFAC. [ABSTRACT FROM AUTHOR]

This work studies the influence of a commercial dispersion of multi wall carbon nanotubes (MWCNT) on the hydration of a class G cement paste, at room and elevated down-hole temperatures. The MWCNT dispersion was produced with a solids concentration of 3.0 % by mass and an anionic surfactant as dispersing agent. Cement pastes with water-to-cement ratio of 0.45 and additions of solid MWCNT by mass of cement up to 0.50 % were studied. Isothermal calorimetry results showed a clear retardation of the hydration of cement caused by the surfactant contained in the MWCNT dispersion. Nevertheless, thermogravimetric evaluations showed that once the hydration reaction resumed, the retardation effect of the surfactant did not have a negative impact on the amount of hydration products precipitated. It was concluded that the commercial MWCNT dispersion presents a good potential to be applied in oil well cement pastes. [ABSTRACT FROM AUTHOR]

In the present study, chemical mapping on the hydration process of cement paste with water-to-cement ( w/c) ratio of 0.60 was implemented by Raman spectroscopy (RS). The RS was applied to study the paste from 12 hours after mixing to 28 days. Cement ingredients and hydration products, including calcium silicates (CS and CS), calcium hydroxide (CH), and ettringite, were quantitatively studied. From the research, it is observed that calcium silicates were consumed gradually with the increased hydration age. Calcium hydroxide increased and tended to cluster in the pore vicinity during hydration. Ettringite was found to form on the surface of the unreacted particles, which was shown as a mixed zone of ettringite and calcium silicates in the maps. It is concluded from the study that chemical mapping was an effective method to assist in visualizing particle dispersion and connection on top of the quantitative analysis. [ABSTRACT FROM AUTHOR]

In the present work, carbon nano/microparticles obtained by controlled pyrolysis of peanut (PS) and hazelnut (HS) shells are presented. These materials were characterized by Raman spectroscopy and field emissionscanning electron microscopy (FE-SEM). When added to cement paste, up to 1 wt%, these materials led to an increase of the cement matrix flexural strength and of toughness. Moreover, with respect to plain cement, the total increase in electromagnetic radiation shielding effect when adding 0.5 wt% of PS or HS in cement composites is much higher in comparison to the ones reported in the literature for CNTs used in the same content. [ABSTRACT FROM AUTHOR]

In the present work, silica nanoparticles (30-70nm) were supplemented into cement paste to study their influence on degree of hydration, porosity and formation of different type of calcium-silicate-hydrate (C-S-H) gel. As the hydration time proceeds, the degree of hydration reach to 76% in nano-modified cement paste whereas plain cement achieve up to 63% at 28 days. An influence of degree of hydration on the porosity was also determined. In plain cement paste, the capillary porosity at 1hr is ~48%, whereas in silica nanoparticles added cement is ~35 % only, it revealed that silica nanoparticles refines the pore structure due to accelerated hydration mechanism leading to denser microstructure. Similarly, increasing gel porosity reveals the formation of more C-S-H gel. Furthermore, C-S-H gel of different Ca/Si ratio in hydrated cement paste was quantified using X-ray diffractometer and thermogravimetry. The results show that in presence of silica nanoparticles, ~24% C-S-H (Ca/Si<1.0) forms, leading to the formation of polymerised and compact C-S-H. In case of plain cement this type of C-S-H was completely absent at 28 days. These studies reveal that the hydration mechanism of the cement can be tuned with the incorporation of silica nanoparticles and thus, producing more durable cementitious materials. [ABSTRACT FROM AUTHOR]

The use of cement as an additive to natural soil has been practiced for a long time in engineering projects. Chemical bonds generated as the result of cement hydration and pozzolanic reactions have been responsible for the increase in strength of cemented soils. The purpose of this research is to evaluate the effect of cement on residual strength of overconsolidated soil. Drained shear strength of overconsolidated compacted soil and soil-cement specimens consisted of 50% bentonite, 50% Aeolian sand with 3% by dry weight cement in as compacted (unsheared or intact); precut (residual) conditions were measured in a direct shear device after varying curing time. The cementation that occurred because of the addition of cement and the increase of curing time caused a remarkable increase of mobilized drained shear strength in both intact and residual conditions. A remarkable increase in cohesion intercepts c', a negligible decrease in φ'(oc) in intact condition, a negligible cohesion and noticeable increase in φ'r, and a decrease in drained shear strength parameters m and mr occurred as a result of cement addition and increased curing time. [ABSTRACT FROM AUTHOR]

Fibers have been used to improve the mechanical and physical properties of cement-based material since the late 1960s. The inclusion of high-dosage and high-aspect ratio microfibers, however, introduces new interfaces between the fiber phase and the matrix phase that may alter the transport properties of fiber cement composites. This paper reports the effects of microbial carbonate precipitation (MCP) on the transport properties of fiber cement composites (FCCs). The results show that the transport properties of untreated FCC increase with fiber dosage as well as fiber aspect ratio due to higher porosity and better pore connectivity. MCP treatment greatly reduced the transport properties of FCC. Scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX) analyses confirm the precipitates were in the form of rhombohedral calcite, which suggests slower MCP due to the growing environment and culturing condition used in this study. [ABSTRACT FROM AUTHOR]

A mathematical model for the transport process of migrating corrosion inhibitor (MCI) in cement-based material and a two-dimensional numerical solution method using commercially-available software are proposed. The numerical analysis results are in a good agreement with experimental data obtained from the two-dimensional absorption tests for nonreactive MCI but do not coincide with the data for reactive MCI. The reason behind may be that the latter reacted with calcium hydroxide (CH) in cement mortar and hindered the transport process. Therefore a modified transport model involving the pore-blocking effect of reactive MCI in cement-based materials is established according to the chemometrics method. The numerical and test results prove that the amendatory model is reasonable to understand the mass transfer of reactive MCI in cement mortar. Variance analyses of the factors in the model are also performed to find the key factor affecting the MCI transport process. A basic transport model and numerical analysis method of MCI in concrete is proposed. The model is corrected involving pore-blocking effect for reactive MCI based on chemical metrology. The numerical calculation results of the proposed model have a fine agreement with experimental results. [ABSTRACT FROM AUTHOR]

The aim of this study was to link the molecular weight (MW) of polycarboxylate superplasticizer (PCE) with the performance of cementitious system for the purpose of developing new products; PCE synthesized by copolymerization of methacrylic acid and methyl poly (ethylene oxide) methacrylate was characterized by proton nuclear magnetic resonance (¹H-NMR) and gel permeation chromatography (GPC). The polycarboylate (PC) was separated into four fractions with different MWs using an ultrafiltration method. The interaction behaviors between PC fractions and cement particles were investigated by measuring the adsorption, zeta potential, and hydration. Results showed that PC fractions with medium MW showed a good dispersion and dispersion retention owing to the adsorption amount continuously increasing with time and delayed the longest cement hydration time. The highest MW of PC exhibited poor dispersion and dispersion retention, having the greatest adsorption amount on the cement surface and poor adsorption capacity in the later period, and carried out to promote hydration of cement compared with other polymers. It can be deduced that there was an ideal MWfor the best different performance of the PC investigated. This can provide an important reference for optimizing the process parameters in the preparation. [ABSTRACT FROM AUTHOR]

In this study, the setting and tensile strength development of ultra-high-performance concrete (UHPC) at a very early age was investigated by performing the penetration resistance test (ASTM C403), as well as the direct tensile test using the newly developed test apparatus, and taking ultrasonic pulse velocity (UPV) measurements. In order to determine the optimum surface treatment method for preventing rapid surface drying of UHPC, four different methods were examined: plastic sheet, curing cover, membrane-forming compound, and paraffin oil. Based on the test results, the use of paraffin oil was found to be the best choice for measuring the penetration resistance and the UPV, and attaching the plastic sheet to the exposed surface was considered to be a simple method for preventing the rapid surface drying of UHPC elements. An S-shaped tensile strength development at a very early age (before 24 h) was experimentally obtained, and it was predicted by a power function of UPV. Lastly, the addition of shrinkage-reducing and expansive admixtures resulted in more rapid development of penetration resistance and UPV of UHPC. [ABSTRACT FROM AUTHOR]

To improve the osteoconductivity of apatite cement (AC) for reconstruction of bone defects after oral maxillofacial surgery, we previously fabricated AC containing atelocollagen (AC(ate)). In the present study, we examined the initial attachment, proliferation and differentiation of mouse osteoblastic cells (MC3T3-E1 cells) on the surface of conventional AC (c-AC), AC(ate) and a plastic cell dish. The number of osteoblastic cells showing initial attachment to AC(ate) was greater than those attached to c-AC and similar to the number attached to the plastic cell wells. We also found that osteoblastic cells were well spread and increased their number on AC(ate) in comparison with c-AC and the wells without specimens, while the amount of procollagen type I carboxy-terminal peptide (PIPC) produced in osteoblastic cells after three days on AC(ate) was greater as compared to the others. There was no significant difference in regard to alkaline phosphatase (ALP) activity and osteocalcin production by osteoblastic cells among the three surface types after three and six days. However, after 12 days, ALP activity and the produced osteocalcin were greater with AC(ate). In conclusion, AC(ate) may be a useful material with high osteoconductivity for reconstruction of bone defects after oral maxillofacial surgery. [ABSTRACT FROM AUTHOR]

A magnesia-phosphate cement (MPC) paste based on magnesia and potassium dihydrogen phosphate (KH2PO4 or PDP) was prepared with the additions of dipotassium hydrogen phosphate (K2HPO4 or DHP) and borax as set-retarders. The resulting materials were characterized in terms of their setting characteristics, strength properties, hydration products, and microstructures. The replacement of PDP by DHP was found to increase the setting time and reduce the intensity of the exothermic reactions during the initial setting and hardening stages. When the replacement percentage did not reach 50%, substitution of dipotassium hydrogen phosphate for potassium dihydrogen phosphate in the MPC paste could strike a good balance between the speedy strength gains and delayed setting time. The setting time of the MPC system increased from 5 min (without DHP addition) to 180 min with PDP replaced by DHP completely. The addition of borax also led to an extension of the initial hardening period, as indicated by reductions in the early values of compressive and flexural strengths. The phase of hydration product analysis indicated that no new phase appeared with the addition of DHP, only that more unreacted magnesia appeared with increasing DHP contents. The microstructural characteristics of the materials produced were strongly dependent on the level of DHP and borax employed. [ABSTRACT FROM AUTHOR]

Inorganic--organic hybrid (IOH) lunar cements are processed by using a lunar soil simulant and polyethylene (PE). As the inorganic simulant grains are strongly held together by the PE binder, the IOH may be utilized as an infrastructural material on the lunar surface. With a uniform simulant grain size, the flexural strength of the IOH decreases exponentially with the binder content, quite close to the strength of samples of random simulant grain-size distribution. If the simulant grains have a two-step size gradation, the IOH strength increases significantly. Above a threshold binder content, the strength decreases only slightly as more simulant grains are added; below the threshold, the IOH becomes much weaker as less binder is used. [ABSTRACT FROM AUTHOR]

An investigation into the behavior of a contaminated clay soil and its treatment was carried out through a program of experimental tests. The contaminated soil samples were prepared with different percentages (3, 6, and 9%) of a glycerol solution with 40% concentration. The samples were prepared as mixtures of clean or glycerol-contaminated soil with different cement contents (3, 6, and 9%). Atterberg limits and unconfined compressive strength (UCS) tests were conducted on the samples. The results showed that Atterberg limits are reduced by adding glycerol or cement or adding glycerol to soil-cement. Both the strength and stiffness of the contaminated soil are reduced by increasing the degree of contamination. The results of treated soil showed that adding cement to contaminated soil increases the strength and the amount of increase in strength is dependent on the percent of cement, curing time and degree of contamination. Based on scanning electron micros- copy analysis, it was found that the presence of glycerol prevents the interaction between soil and cement. [ABSTRACT FROM AUTHOR]

According to former President of Petrobrás, Maria das Graças Silva Foster, in 2013 the Brazil produced about 1 million barrels per day, that is, much of the nation's economic demand is subject to extraction of oil, what determines the country scientific investments for the Betterment of this economic mode, in order to maximize the extraction and prevent environmental damage. On the extraction of oil in the drilling process, a step that is required is the cementing of the well. The cement used in the process is subject to strict conditions of temperature and pressure, and must support fragile and porous rocks, fluids corrosive and pressurized. Therefore, it is necessary to check the rheological behavior of cement paste. This work aims to evaluate the study of rheology and rotational dynamics in cementing oil wells. It is therefore important to improve the homogeneity of the cement and ceramic suspensions because they lose these characteristics when subjected to the transport, mixing and pumping. Was held the addition of minerals and additives in the folder for the oil well cement in accordance with the regulations in force, with the implementation of models of Bingham and dynamic power or oscillatory. Where was evaluated by testing the determination of the potential for speed and tests zeta compression and mechanical traction. Evaluated by testing for developers and rheological tests to determine zeta potential of more than 30 mV being the same stable and mechanical compression and traction test. [ABSTRACT FROM AUTHOR]

The Frattini test and strength activity index (SAI) test have been commonly used methods to assess the pozzolanic activity of pozzolan by measuring its reaction extent, which would be affected by the sulfate content in pozzolan and the cement used. This study investigates the effect of sulfate content in sulfate-rich fly ash on the test results regarding pozzolanic activity by means of the Frattini test and SAI test; three fly ashes with different sulfate contents are used and their sulfate contents are further increased by adding calcined gypsums. There is significant correlation between the test results of the pozzolanic activity and the sulfur trioxide content of the cement-fly ash system, no matter whether the sulfates came from cement or fly ash. However, current methods may confound the test results regarding the pozzolanic activity of sulfate-rich fly ash. It is suggested that the sulfur trioxide content of the cement-fly ash system should be kept constant when the Frattini test and SAI test are selected to evaluate the pozzolanic activity of sulfate-rich fly ash or to compare with other fly ashes and pozzolans. [ABSTRACT FROM AUTHOR]

This study examined the effects of magnesium sulfate and sodium sulfide on fresh and hardened cement mortar. Two 410 kg/m3 dosed mortars were produced (water/cement ratios of 0·63 and 0·72). Sulfate salt solutions were prepared in different concentrations and used as mixing water. Solutions of magnesium sulfate and sodium sulfide and reference mortars were prepared with 1 l of mixing and drinking water, respectively. Mortars were produced in 26 (2 × 13) different mixtures. From each mixture, eight samples were produced for shrinkage and other tests. The workable life of the mortars was determined by vibratory table experiments. Experiments were conducted using a Vicat apparatus to determine the effects of the tested chemical substances on setting duration. For each mixture, six samples were held in water at a temperature of 20 ± 2°C until the day of testing. Bending and compression tests were then performed on samples aged 7, 28 and 90 d (two samples per age). For shrinkage tests, size changes of the two samples were measured until the 90th day of holding in a controlled environment (21°C and 55%-65% humidity). The effects of sulfate salts on fresh and hardened concrete mixes were analysed. The results revealed that magnesium sulfate was the most detrimental, but also showed that sodium sulfide increased the compressive strength. [ABSTRACT FROM AUTHOR]

The reduced lifetime of geothermal wells is one of the main issues facing the geothermal industry, with cement durability being one of the main causes for shortening of a well's life. While most wells are cemented with American Petroleum Institute (API) class cements, alternative cementing systems are currently being considered. In this paper, the interactions of two alternative cement formulations with a typical geothermal rock formation are compared with a class A cement. This allows understanding of the most critical zone in the geothermal cement, which is the outermost layer where the cement encounters and, consequently, interacts with the exterior harsh environment, including the volcanic formation and brine. The faster setting of white cement and high-alumina cement compared with the well Portland cement seems to reduce the reaction extent with the rock. For all the cements tested, both the increased curing temperature (from 150°C to 290°C) and the use of bentonite as drilling mud significantly decreased the bond between the cement and the rock. [ABSTRACT FROM AUTHOR]

The sequence structure of polymers plays an important role in determining their performance. However, existing polycarboxylates mostly have a broad molecular weight distribution and the sequence structure is randomly distributed. In this work, a novel water-soluble block copolymer made of poly(ethylene glycol) methyl ether methacrylate (OEGMA) and acrylic acid (AA) was designed using reversible addition-fragmentation chain transfer polymerisation. Structural information of the block polycarboxylate was characterised by gel permeation chromatography and proton nuclear magnetic resonance. The effects of molar ratio of AA to OEGMA on flowability, zeta potential and adsorption in cement paste were studied. It was proved that polycarboxylate with a block distribution could be successfully applied as a superplasticiser. Furthermore, the length of the two blocks in the block distribution influenced the zeta potential and adsorption of the superplasticiser onto cement particle surfaces, and thereby the workability of cementitious materials. The knowledge gained from this work may be used in the design of superplasticisers for optimal performance in some specific applications. [ABSTRACT FROM AUTHOR]

Alkali–silica reaction expansions are disturbed by a variety of mechanisms (alkali leaching, ASR-gel permeation through cracks, chemical conditions in pore solution water and its dependence on temperature). An important consequence is the difficulty of using the expansion test on specimens to analyse the behaviour of ASR-damaged structures. The paper focuses on the influence of leaching: alkali transport and consumption are modelled using a multi-scale approach (aggregate and concrete scales). The evaluation of the alkali concentration below which expansion stops is needed to perform relevant analysis in various alkali conditions and this alkali threshold is quantified according to calcium concentration and temperature. The impact of the coupling between alkali transport in aggregate and silica reactivity is also studied. Lastly, the consequences of leaching on ASR-expansion are analysed in two case studies drawn from the literature. [ABSTRACT FROM AUTHOR]

The effect of the combination of fly ash and silica fume on the water resistance of Magnesium–Potassium Phosphate Cement (MKPC) was investigated, and the improvement mechanism was discussed based on the micro-analysis of XRD, FSEM and pore structure. The results indicate that, the physical effect of the combination of fly ash and silica fume on MKPC is dominated compared with the chemical effect because of the optimization of pore structure. The combination of fly ash and silica fume leads to higher density and later-age compressive strength of MKPCs compared to those without fly ash and silica fume under air curing and water curing, respectively. The strength retention ratios (namely water resistance) of MKPCs with the combination of fly ash and silica fume at 56 days are found to be significantly higher than those without fly ash and silica fume. [ABSTRACT FROM AUTHOR]

Cement production is characterized by extremely high energy consumption per unit of product. Energy costs and environmental standards encouraged cement manufacturers worldwide to evaluate to what extent conventional fuels can be replaced by alternative fuels, i.e., processed waste materials, such as scrap tires. The decisive factors promoting the use of cement kilns for the utilization of scrap tires are: the high incineration temperature, the large area of the furnace, the significant length of the kiln, the long period of time the fuel stays inside the kiln, and the alkaline environment inside the kiln. The use of scrap tires in cement kilns is one of the best technologies for a complete and safe destruction of these wastes, due to the fact that there is a simultaneous benefit of destroying wastes and getting the energy. Thus, the use of scrap tires as alternative fuel in cement kilns has energy and economic justifiability, and it is environmentally friendly. In this article, monitoring results of nitrogen and sulfur oxides emissions from cement kilns in a cement factory in Serbia are given, depending on the ratio of scrap tires in total fuel quantity. Research was carried out for 0 to 15% share of scrap tires in total heat production. Nitrogen and sulfur oxides emission measurements from cement kilns were done during a trial use of scrap tires as a secondary fuel in a cement factory. During nitrogen and sulfur oxides emissions monitoring from the cement kiln, coal and petroleum coke were used as primary fuel, and whole or shredded tires were used as secondary fuel. Experimental results have shown the encouraging results: in particular, clinker characteristics were unmodified, and stack emissions of NOx and SO2were, in the case of tires, slightly decreased, in some cases were incremented, but remaining always below the law imposed limits. [ABSTRACT FROM PUBLISHER]

In spite of not being legally accepted in most countries, mixed recycled aggregates (MRA) could be a suitable raw material for concrete manufacturing. The aims of this research were as follows: (i) to analyze the effect of the replacement ratio of natural coarse aggregates with MRA, the amount of ceramic particles in MRA, and the amount of cement, on the mechanical and physical properties of a non-structural concrete made with a low cement content; and (ii) to verify if it is possible to achieve a low-strength concrete that replaces a greater amount of natural aggregate with MRA and that has a low cement content. Two series of concrete mixes were manufactured using 180 and 200 kg/m³ of CEM II/A-V 42.5 R type Portland cement. Each series included seven concrete mixes: one with natural aggregates; two MRA with different ceramic particle contents; and one for each coarse aggregate replacement ratio (20%, 40%, and 100%). To study their properties, compressive and splitting tensile strength, modulus of elasticity, density, porosity, water penetration, and sorptivity, tests were performed. The results confirmed that the main factors affecting the properties analyzed in this research are the amount of cement and the replacement ratio; the two MRAs used in this work presented a similar influence on the properties. A non-structural, low-strength concrete (15 MPa) with an MRA replacement ratio of up to 100% for 200 kg/m³ of cement was obtained. This type of concrete could be applied in the construction of ditches, sidewalks, and other similar civil works. [ABSTRACT FROM AUTHOR]

The main objective of this research is to investigate the feasibility of using the residual powder obtained from organic waste to replace a part of Portland cement during concrete production. The chemical and physical properties of the organic residual powder were first investigated using scanning transmission electron microscopy (STEM) and energy dispersive X-ray spectroscopy (EDS). The replacement ratios of cement have also been studied for 0%, 5%, 10%, 15%, and 20% of the residual powder by weight. Moreover, we evaluated the compressive strength, specific gravity, water absorption, and voids content of the concrete specimens that were modified with different concentrations of the residual powder. Results indicate that 5% residual powder concentration resulted in better physical and mechanical properties of the modified concrete when compared with the reference concrete. At this concentration, the addition of residual powder act as fillers in concrete, reducing the amount of voids and causing a higher density in the material. [ABSTRACT FROM AUTHOR]

To predict the behavior of the cement sheath after CO2 injection and the potential for leakage pathways, it is key to understand how the mechanical properties of the cement evolves with CO2 exposure time. We performed scratch-hardness tests on hardened samples of class G cement before and after CO2 exposure. The cement was exposed to CO2-rich fluid for one to six months at 65 °C and 8 MPa P(olal. Detailed SEM-EDX analyses showed reaction zones similar to those previously reported in the literature: (l) an outer-reacted, porous silica-rich zone; (2) a dense, carbonated zone; and (3) a more porous, Ca-depleted inner zone. The quantitative mechanical data (brittle compressive strength and friction coefficient) obtained for each of the zones suggest that the heterogeneity of reacted cement leads to a wide range of brittle strength values in any of the reaction zones, with only a rough dependence on exposure time. However, the data can be used to guide numerical modeling efforts needed to assess the impact of reaction-induced mechanical failure of wellbore cement by coupling sensitivity analysis and mechanical predictions. [ABSTRACT FROM AUTHOR]

Stratlingite, Ca4Al2(OH)12[AlSi(OH)8]2·2H2O, is an AFm phase which appears as a hydration product of aluminium-rich cements. These binders may be calcium aluminate cements, calcium sulfoaluminate cements and also belite calcium sulfo-aluminate (BCSA) cements. The structure of stratlingite is known from single-crystal studies of tiny minerals but their bulk formation, crystal structure and microstructure of powders is poorly understood. This paper reports on the synthesis of stratlingite and a complete structural and microstructural characterisation by synchrotron X-ray powder diffraction, nuclear magnetic resonance, scanning electron microscopy and thermal analyses. The structural and microstructural models have important implications for a correct quantitative phase analysis of stratlingite in cement pastes (for instance, in pastes of BCSA cements). The microstructure of stratlingite formed in cement pastes is highly dependent on the hydration conditions. In BCSA pastes, the (003) line position of stratlingite appears slightly shifted towards higher diffracting angles (lower inter-layered distance) after stopping hydration compared to that of a similar phase present in a paste analysed without stopping hydration. This is related to dehydration and disorder. This shift and peak broadening is even larger when the paste has suffered partial dehydration during curing (apart from stopping hydration). A microstructural study is presented. [ABSTRACT FROM AUTHOR]

Two cement pastes (water to cement ratio, w/ c = 0·5, 0·3) were investigated through mercury intrusion porosimetry (MIP) and nitrogen adsorption/desorption (NAD) methods at different hardening ages. The pore structure is characterised by specific surface area, pore volume and pore size distribution. The results show that: ( a) the pore structure has strong scale dependence and NAD-MIP joint measurement helps to identify the different pore structure patterns; ( b) MIP total pore volume captures the global process of the hydrates filling process with curing age, the mesopore (2-70 nm) volume is dominated by hydrates filling for w/ c = 0·5 but countered by high-density calcium-silicate-hydrate growth for w/ c = 0·3; ( c) specific surface area is sensitive to calcium-silicate-hydrate growth and specific surface area values are likely to confirm that high w/ c (0·5) favours low-density calcium-silicate-hydrate growth whereas low w/ c (0·3) facilitates high-density calcium-silicate-hydrate formation. [ABSTRACT FROM AUTHOR]

The influence of the water phase of an asphalt emulsion on cement hydration is investigated. In addition, the effect of possible components in the water phase is studied and results are compared with those of the water phase. Results indicate that it is the addition of cationic emulsifier lignin-amine that retards cement hydration, prolongs its induction period and reduces maximum hydration heat. However, non-emulsifier alkylphenol polyoxyethylene and hydrochloric acid only reduce maximum heat. No significant differences exist in terms of calcium hydroxide content and non-evaporable water content between the plain cement paste and cement paste with the aforementioned chemical components. Zeta potential results show that the adsorption of lignin-amine on the cement grains is quite different from that of superplasticiser. Although cement hydration and calcium hydroxide crystal growth are retarded with the addition of lignin-amine, calcium hydroxide crystals are fully developed and thus show a strengthened diffraction peak. [ABSTRACT FROM AUTHOR]

The aim of this study was to identify interaction mechanisms among particles in the hydration of pozzolan cements. To this end, chemical, physical, mineralogical and electrokinetic analyses of samples were conducted. Furthermore, free surface energy components were defined by Van Oss, Chaudry and Good equations and the contact angle values of samples were determined by using the thin layer wicking method. The results show that the addition of water turns solid-air interfaces into solid-liquid interfaces (wetting), while attraction and repulsion take place depending on the electrical charges on particle surfaces. While total surface energy and components of particles seek to attain balance as a result of wetting, hydration and pozzolanic reactions occur. [ABSTRACT FROM AUTHOR]

Purpose – The purpose of this paper is to determine if a type of cactus mucilage, Opuntia ficus-indica (OFI), may act as a corrosion inhibitor for carbon steel in cement-based materials (mortar) exposed to chloride-laden environment. Design/methodology/approach – Mortar prisms, reinforced with carbon steel rods, were immersed in sodium chloride (NaCl) solution for five wet – dry cycles. The experimentation included electrochemical monitoring (corrosion potential, Ecorr, and polarization resistance, Rp) of carbon steel during the time of exposure until corrosion-induced cracking appeared at the mortar surface. Crack survey on the mortar prisms was performed. Carbon steel rods were retrieved from the mortar after crack survey and steel mass loss at the end of the experimental period was estimated. A comparison between the different mixtures was also performed. Findings – OFI mucilage did perform as a corrosion inhibitor of steel in chloride contaminated mortar. Research limitations/implications – The experimental program needs to be corroborated in concrete specimens with typical dimensions. The surface oxide/hydroxide formation of the carbon steel in contact with the OFI mucilage is still unknown; thus, electrochemical impedance spectroscopy (EIS) and X-ray diffraction (XRD) analyses are needed. Practical implications – OFI mucilage is a suitable natural product that can be used to increase durability of concrete structures not only in countries where OFI cactus is produced, but also in many other countries where this plant is considered a plague. Originality/value – The new information obtained from this paper is the innovative use of a by-product of this cactus plant for construction industry applications. [ABSTRACT FROM AUTHOR]

In the present study, pure and mixed calcium phosphate/gypsum cements were prepared and characterized. Chara-cterizations were performed using X-ray diffraction FTIR spectroscopy, thermogravimetric analysis, and Scanning Electron Microscopy. Furthermore, the mechanical proper-ties of the materials were studied and it was found that they depend with the gypsum content. Bioactivity tests after incubation in 2xSBF solution revealed dense apatite structure on the samples containing α-tricalcium phosphate while the pure gypsum specimens showed sparse distributed tiny apatite crystals. Finally, 1% and 2% wt of the anti-inflammatory drug ibuprofen incorporated into the cement paste and the release behaviour of the drug was stu-died for 18 days in PBS solution. The results showed marked differences in the release profiles of ibuprofen for the different formulations. Complete release of the drug was noticed in the case of pure calcium phosphate cements within 18 days whereas ca. 35-40% of the drug was released from its congeners containing gypsum at the same timescale. [ABSTRACT FROM AUTHOR]

Cement pastes and mortars based on ordinary Portland cement containing nitrogen-doped multiwalled carbon nanotubes (MWCNT-Nx) or oxygen-functionalized multiwalled carbon nanotubes (MWCNT-Ox) are investigated. To incorporate MWCNTs into the cementitious matrix, the as-produced carpets are dispersed over periods of 1 and 2 hours in distilled water at pH levels of 1 and 7. The cement pastes are prepared by adding 0.1 wt% of MWCNTs to cement powder, followed by characterization with SEM and X-ray diffraction (XRD) at an early age (first hours of hydration). The mortars are mechanically characterized during the hydration process for a period of 28 days. SEM characterization of cement pastes revealed that the carbon nanotubes are well incorporated in the cementitious matrix, with the hydrated cement grains interconnected by long carbon nanotubes. XRD characterizations demonstrated that, during the hydration of cement pastes, different peaks emerged that were associated with ettringite, hydrated calcium silicate, and calcium hydroxide, among other structures. Results of the compressive strength measurements for mortars simultaneously mixed with MWCNT-Nx and MWCNT-Ox reached an increment of approximately 30% in compressive strength. In addition, density functional theory calculations were performed in nitrogen-doped and oxygen-functionalized carbon nanotubes interacting with a cement grain. [ABSTRACT FROM AUTHOR]

Concrete is a very complicated, random, multi-scale and multi-phase material. It is important to know cement paste structure to understand its properties and damage mechanisms that can influence the properties of concrete. Recently, many researchers have focused on the simulation of hydrated cement microstructure to figure out how damage/deterioration might be initiated. Moreover, as the microstructure of hydrated cement is known, we are able to produce greener, stronger and more durable concrete. There is a critical need to survey previous research to direct future study. In recent years due to development of advanced computers, most researchers tend to study the atomistic structure of hydrated cement and to make a bridge between nano and macro scales. Various models have been developed to simulate cement structure. This paper is an introductory review of the most important studies proposed by researchers for simulation of hydrated cement at different scales varying from nano to macro. Impact of the latest advances in simulation methods and their applications for hydrated cement research is investigated. Salient issues are categorised into four main sections including numerical models, microstructural models for cement hydration simulation, atomistic simulations and multi-scale studies. [ABSTRACT FROM AUTHOR]

The present article show the structural analysis realized to metallic silo for storage cement through of the parametric model development in the finite element software ASNYS APDL, the fill and discharge pressures applied on the silo wall is determined with the Eurocode normative EN 1991-4.The model is development with type shell elements allowing that the structure silo fits to the cylindrical and conical geometric of the silo. It explains each of the phases having the development of the model and is made a detailed analysis of the results delivered by the software; different models are evaluated changing the sheet thickness for select the most appropriate. Also the results are analyzed when be changing the tilting the hopper and is reviewed the behavior of the silo when is analyzed with its structure. [ABSTRACT FROM AUTHOR]

Filled-pozzolanic cement pastes were made by different replacements of OPC by electric arc furnace slag (EAFS) with silica fume (SF) at water/cement ratio of 0.27. The pastes were hydrated up to 90 days. At each time interval, the physico-chemical characteristics of the hardened cement pastes were studied and related to the structure of the hardened pastes and the role of EAFS replacement as a filler in the hardened OPC-EAFS pastes. It was found that the optimum replacement of OPC by EAFS for the improvement in hydraulic properties of filled cement pastes is 6%. High replacement of OPC by EAFS (10% or 15%) causes a notable deterioration in the compressive strength at all ages of hydration. The replacement of EAFS in Mix (90% OPC + 10% EAFS) by 4% SF causes a marked improvement in the mechanical properties for the hardened pastes of Mix (90% OPC + 6% EAFS + 4% SF). The DSC thermograms for all pastes indicated the formation of nearly amorphous calcium silicate hydrates, calcium sulphoaluminate hydrates, calcium aluminate hydrates and portlandite. The SEM micrographs showed that the partial substitution of OPC by EAFS and/or SF leads to more dense structures as compared to the neat OPC paste. [ABSTRACT FROM AUTHOR]