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This paper explores the development of 3D-printed self-sensing Ultra-High Performance Concrete (UHPC) by incorporating graphite (G) powder, milled carbon microfiber (MCMF), and chopped carbon microfiber (CCMF) as additives into the UHPC matrix to enhance piezoresistive properties while maintaining workability for 3D printing. Percolation curves were established to identify optimal filler inclusion levels, and a series of compressive tests, including quasi-static cyclic, dynamic cyclic, and monotonic compressive loading, were conducted to evaluate the piezoresistive and mechanical performance of 29 different mix designs. It was found that incorporating G powder improved the conductivity of the UHPC but decreased compressive strength for both mold-cast and 3D-printed specimens. However, incorporating either MCMF or CCMF into the UHPC resulted in the maximum 9.8% and 19.2% increase in compressive strength and Young's modulus, respectively, compared to the plain UHPC. The hybrid combination of MCMF and CCMF showed particularly effective in enhancing sensing performance, achieving strain linearity over 600 μ ε . The best-preforming specimens (3G250M250CCMF) were fabricated using 3 wt% of G, 0.25 wt% of MCMF, and 0.25 wt% of CCMF, yielding a maximum strain gauge factor of 540, a resolution of 68 μ ε , and an accuracy of 4.5 μ ε under axial compression. The 3D-printed version of the best-performing specimens exhibited slightly diminished piezoresistive and mechanical behaviors compared to their mold-cast counterparts, yielding a maximum strain gauge factor of 410, a resolution of 99 μ ε , and an accuracy of 8.6 μ ε . [ABSTRACT FROM AUTHOR]

Fracture behavior is an important issue to consider when analysing and designing important concrete structures. Fracture behavior is dependent on the characteristics and materials percentage in concrete. Thus, due to the application of polyvinyl alcohol fiber, this type of concrete's structure and fracture behavior will differ from normal concrete. This investigation aims to determine some mechanical properties, in addition to the fracture parameters corresponding to low and medium compressive resistance of engineering cementitious composite concrete reinforcing by fiber for notched and un-notched beams, using size effect model techniques in contrast to conventional concrete. The outcomes illustrate an increment in modulus of rupture; both fracture energy and fracture toughness, which were incremented. At the same time, the nominal stress reduction of the notched-beam is superior to un-notched beam. Five mixes for each strength grade were cast to test fresh and hardened properties; the optimum mixture that gave the higher modulus of rupture was chosen for fracture parameters investigations. Two engineering cementitious concrete mixtures containing 1.5% and 2% polyvinyl fiber for grades M25 and M65, respectively, obtained higher modulus of rupture. Geometrically, three (75×75×400) mm, (75×150×800) mm, and (75×200×1200) mm notched-beams were investigated by applying one central point load for testing their fracture toughness, fracture energy, and characteristics length, also the influence of tensile ductility of engineering cementitious concrete. The denser interfacial transition zone of engineering cementitious concrete had the highest fracture toughness and a ductile behavior of mode of failure with a flatter fracture plane than conventional concrete. The higher fracture toughness value was observed on (M25-BC3) and (M65-BC2). Outcomes indicate that conventional concrete exhibited greater sensitivity to size effect parameter due to its poorer tensile ductility than concrete incorporating polyvinyl alcohol fiber. [ABSTRACT FROM AUTHOR]

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The basic chemical properties of mining and metallurgical waste slag and raw materials are measured, and compound strong alkaline activator is developed according to the test results, which can be used to activate the activity of mining and metallurgical waste slag, so as to prepare special backfill cementitious material. The hydration reaction products in the backfill were tested by XRD. The results showed that the main hydration products supporting the strength of backfill were ettringite (AFt), calcium hydroxide (CH), aluminum glue(AH8_10), calcium silicate hydrate(C S H), hydrated calcium aluminosilicate(C A S H), et al. The formation of one ettringite(AFt) molecule will bind and adsorb 32 H2 0 molecules, indicating that the special backfill cementitious material is more suitable for backfill slurry with larger water content. At the same time, SEM was used to analyze the internal structure of the backfill at different ages, revealing the strength growth law of the backfill, and analyzing the strength mechanism of the backfill at each stage. The strength of backfill of two kinds of cementitious materials was tested by strength test under different conditions. The results showed that the strength of backfill prepared by special cementitious materials(KS) was higher than that prepared by cement (SN), there was a one fold difference in the strength value. [ABSTRACT FROM AUTHOR]

The properties of a large number of concrete infrastructures in China are deteriorating year by year, raising the need for repairing and strengthening these infrastructures. By introducing waterborne polymers into a cement concrete system, brittle cracks and easy bonding performance defects of concrete can be compensated for to form a long-life, semi rigid, waterborne polymer-modified cementitious repair material with a promising development prospect. This paper investigates the modification effect of polymer emulsions on ordinary cement mortar. Our research mainly focused on the physical and mechanical properties, durability, microstructure and application status of waterborne polymer-modified cementitious composites. Literature studies show that with the increase in waterborne polymer content (0 wt%~20 wt%), the performance of cement mortar significantly improves, which in turn expands its application range. Compared with ordinary cement mortar, the introduction of waterborne polymers blocks some of the pores in the cement to a certain extent, thus improving its permeability, freeze–thaw resistance and durability. Finally, this paper describes the application of waterborne polymer–cementitious composites in western saline soil environments, as well as discusses the prospects of their development. [ABSTRACT FROM AUTHOR]

This study examines the properties of cementitious composites incorporating volcanic ash (VA) and dune sand. The effect of five mix design parameters was studied using the Taguchi method. The fresh, mechanical, and durability properties of sixteen mixes were evaluated. To convert the evaluation from single criterion to multi-criteria, a hybrid Taguchi-TOPSIS was employed. Results showed that the optimum composite mix was made with a binder content of 500 kg/m3, a water-to-binder ratio of 0.5, VA replacement of 20%, dune sand replacement of 20%, and SP content of 0.75%. The optimum mix had a flow, final setting time, 28-day compressive strength, volume of permeable voids, and calcium leaching strength retention of 175 mm, 440 min, 50.5 MPa, 11.3%, and 78.8%, respectively. Portlandite, tobermorite, and gismondine were characterized as hydration products, while calcite and dolomite were also detected. This work provides an advanced understanding of the impact of mix design parameters on various properties while optimizing their levels for superior performance.

By designing different steam curing systems and comparing the changes law of compressive strength of low-carbon cementitious materials, optimum suitable steam curing system for low-carbon cementitious materials can be obtained. The results indicate that for solid waste based low-carbon cementitious materials, the early strength can be improved by using a waiting time the same as the induction period during steam curing. For steam curing temperature and steam curing time, 65 °C and 12 hours is sufficient to achieve ideal early strength, the compressive strength can not be improved significantly by longer steam curing time and higher steam curing temperature. [ABSTRACT FROM AUTHOR]

The properties of a large number of concrete infrastructures in China are deteriorating year by year, raising the need for repairing and strengthening these infrastructures. By introducing waterborne polymers into a cement concrete system, brittle cracks and easy bonding performance defects of concrete can be compensated for to form a long-life, semi rigid, waterborne polymer-modified cementitious repair material with a promising development prospect. This paper investigates the modification effect of polymer emulsions on ordinary cement mortar. Our research mainly focused on the physical and mechanical properties, durability, microstructure and application status of waterborne polymer-modified cementitious composites. Literature studies show that with the increase in waterborne polymer content (0 wt%~20 wt%), the performance of cement mortar significantly improves, which in turn expands its application range. Compared with ordinary cement mortar, the introduction of waterborne polymers blocks some of the pores in the cement to a certain extent, thus improving its permeability, freeze–thaw resistance and durability. Finally, this paper describes the application of waterborne polymer–cementitious composites in western saline soil environments, as well as discusses the prospects of their development.

The importance of nanomaterials has been known for many years, but their usage in cement and concrete production is not accelerated and emphasized extensively. Cement and concrete are the base input material for the construction industry, and the industry is facing tremendous pressure to reduce its greenhouse gas emission (GHG); in 2021, the cement industry emitted about 7% GHG, equal to 2.5 Giga Ton gases of global GHG emission. It is estimated that by enhancing various supplementary cementitious materials (SCM), approximately 9% of the GHG emission of the cement industry can be reduced globally. It is also known that the cement hydration process is very sensitive and altered by many factors such as temperatures, amount of water, surface area, chemical properties, mineral phases, and type of SCM used. The alteration of hydration has adverse influences on cement and concrete performance. Nanomaterials can play an essential role by offsetting the adverse effects of high usage of SCMs in the cement, helping in increasing sustainability by reducing the intensity of CO2, and offering value-added features like self-sensing self-cleaning, antibacterial, anti-fungal, anti-algae, and antistain in the cement other than cement strength, which may promote the use of blended cement and replace ordinary Portland cement in the construction industry. This comparative review aims to understand nanomaterials' advantages and challenges and compare their role and their influence on the cement hydration process based on the types of nanomaterials and their nature as Pozzolanic Nanomaterial (nano SiO2, nano MgO, Nano CaCO3, Nano Metakaolin), Metal oxide Nanomaterial (nano TiO2, nano CuO, nano ZnO, nano Al2O3, nano Fe2O3) and Carbon Based Nanomaterial (Carbon Nanotubes CNTs, Carbon Nano Fibers CNFs, Graphene Oxides). [ABSTRACT FROM AUTHOR]

To achieve the new level of blended cement performance, the slurries of Class C and F fly ash were mechano-chemically activated in a vibro-mill with superplasticizer and nanosilica. The resulting activated products were tested in mortars replacing up to 30% portland cement. The activation process resulted in the formation of nano-seed clusters and micronized ash particles that both significantly improve the early strength of mortars as well as allow for the replacement of portland cement with industrial by-products. A small amount, 0.1% (of a binder weight), of nanosilica was used in selected compositions to improve the process of activation and facilitate the formation of nano-seeds. Due to an intensive activation of fly ash in the vibro-mill and the formation of nano-seed hydration products, the increase in the heat of the hydration flux and improvement of the mechanical properties such as compressive strength, especially in the early stages of hardening, were achieved. It is envisioned that fly ash activation and the use of supplementary cementitious materials as a precursor can induce a denser structure of cementitious matrix due to better particle packing realized with the application of the nano-seed product, nanosilica, ultra-fine particles of fly ash, and the formation of a refined C-S-H structure realized with the incorporation of the nano-seed particles. [ABSTRACT FROM AUTHOR]

The purpose of this study is to investigate the healing performance of solid capsules made of cement as a basis for manufacturing self-healing capsules that can heal cracks in cementitious composites. The solid capsules were mixed with 5%, 10%, and 15% concentrations on the cement. The self-healing performance of cementitious composites with solid capsules was investigated through three evaluations. First, the mechanical strength-healing performance was evaluated through a re-loading test. Second, the durability-healing performance was evaluated through a permeability test. Finally, the crack-healing performance was examined by observing the crack widths. Through evaluation of the healing performance of the solid capsules, the healing performance of the compressive strength was found to be high when the capsule proportion was 10% and its size was within the range of 300 μm to 850 μm. Furthermore, the splitting tensile strength showed a high healing performance when the capsule proportion mixed was 15% and its size was 850 μm. In the case of the permeability test, a capsule size of 850 μm showed a healing effect greater than 95%. Cracks with a width of up to 200 μm tended to heal using capsules with a size of 600 μm to 850 μm. [ABSTRACT FROM AUTHOR]

This paper examines the effectiveness of using carbon fabric-reinforced matrix (C-FRM) composites to improve the shear response of reinforced concrete (RC) deep beams. Ten RC deep beams were tested. Test variables included the presence of internal steel stirrups, number of C-FRM layers, angle of inclination of the second layer of C-FRM, and type of matrix. In the absence of minimum steel stirrups, the use of one layer of C-FRM with cementitious and geopolymeric matrices resulted in 95% and 77% shear strength gains, respectively. Increasing the number of C-FRM composites to two layers insignificantly increased the shear strength gain. Positioning the second layer of C-FRM in the vertical direction tended to be more effective than placing it in the horizontal direction. The gain in the shear capacity was less pronounced in the presence of steel stirrups, where a maximum shear strength gain of 18% was recorded. Numerical models were developed to predict the shear response of the tested beams. Outcomes of the numerical modeling were in good agreement with those obtained from the tests. The inclusion of a bond–slip law at the fabric–matrix interface insignificantly reduced the predicted shear strength. The ratios of the predicted-to-measured shear capacity of the models with and without the bond–slip law were, on average, 0.90 and 0.95, with corresponding standard deviations of 0.09 and 0.11, respectively. [ABSTRACT FROM AUTHOR]

Significant research has been done in recent decades in the field of the dispersion of carbon nanotubes in aqueous solutions and the reinforcement of ordinary Portland cement (OPC). However, the cementitious mixture, as an alkaline environment, easily leads to the re-agglomeration of dispersed single-walled carbon nanotubes (SWCNTs) and influences their enhancing effects. Humic acid (HA) is a type of natural organic matter which can assist the stabilization of dispersed single-walled carbon nanotubes in cementitious composites. The present study characterizes the influence of HA in stabilizing the dispersion of SWCNTs by means of ultraviolet spectrophotometer tests. The fluidity of fresh cement slurry and mechanical performance of hardened OPC pastes were measured to better illustrate the dispersion of SWCNTs in real cement composites. The results not only reveal that the addition of an alkaline environment to the SWCNT suspensions results in a rapid decrease of the dispersion, but also suggest that the appropriate content of HA (0.12 wt.%) can play a significant role in stabilizing the dispersion of SWCNTs. When the mixed hybrid of SWCNTs and HA with a concentration of HA/c equal to 0.05 wt.% is used, the fluidity of the fresh cement slurry experiences a maximum decline and this mixture content of materials will dramatically increase the compressive and flexural strength by about 31% and 48%, which indicates that more SWCNTs are in a dispersed state under this concentration. SEM images further prove that a suitable HA/c can inhibit the expansion of cracks in the cementitious composites.

Abundant aquatic animal by-products are available in Nigeria which include clam, oyster, rock Snail and periwinkle shells. These are usually dumped on open lands without any economic value after fleshy parts of these animals had been consumed by humans, hence, result into environmental problems. In the agricultural sector, Rice husk and Palm oil fuel ashes are by-products from rice and palm oil industries after the husks have been used as source of fuel. Disposal of these wastes are always a major issue as they constitute nuisance to the environment. This research has collected and characterized these wastes in the laboratory to ascertain their suitability as supplementary cementitious materials. With this study, physical properties such as particle size, specific gravity, specific surface area and morphology are conducted by Scanning Electron Morphology, SEM; chemical analysis are carried out with the aid of X-ray Fluorescence (XRF), for microstructure examination, X-ray Diffraction (XRD) machine is used for detecting minerals in the materials while Field Emission Scanning Electron Microscopy and Energy-Dispersive X-ray analysis (FESEM-EDX) are used for image and element detection. The results of these analyses will help in the future work of pozzolanic and geopolymer construction in Nigeria. The results are further compared with previous literature to see their compatibility and discrepancy.

This paper presents the tensile stress strain model of a recyclable polyvinyl chloride/calcium carbonate (PVC/CaCO3) thermo-formable, fire/water proof resistant, and durable composite mineral plank. The paper presents experimentally obtained material stress-strain properties in direct tension as a function of its parameters including thickness, surface texture and grain alignment. With an increase in thickness from 1 mm (0.039 in.) to 12 mm (0.47 in.) for rough surface texture and parallel grain alignment, tensile and rupture strengths decreased from 27.4 MPa (4.11 ksi) to 14 MPa (2.1 ksi) and from 14 MPa (2.1 ksi) to 6 MPa (0.9 ksi) respectively. Strains at rupture increased from 0.01 to 0.02 while the modulus of elasticity decreased from 23078 MPa (3462 ksi) to 2139 MPa (320.85 ksi). Smoothness of surface texture increased the ultimate and rupture stresses by 16% while rupture strains increased by 45% leading to a more ductile material. Grain orientation perpendicular to the load direction resulted in an 18% reduction in ultimate strength. The paper proposes models for predicting the stress strain relationship including modulus of elasticity, toughness, stress and strain in the proportional, ultimate and rupture states in terms of the material parameters. The developed models are essential for establishing code requirements and design criteria for structural members retrofitted with this type of composite.

The purpose of this study is to investigate the healing performance of solid capsules made of cement as a basis for manufacturing self-healing capsules that can heal cracks in cementitious composites. The solid capsules were mixed with 5%, 10%, and 15% concentrations on the cement. The self-healing performance of cementitious composites with solid capsules was investigated through three evaluations. First, the mechanical strength-healing performance was evaluated through a re-loading test. Second, the durability-healing performance was evaluated through a permeability test. Finally, the crack-healing performance was examined by observing the crack widths. Through evaluation of the healing performance of the solid capsules, the healing performance of the compressive strength was found to be high when the capsule proportion was 10% and its size was within the range of 300 μm to 850 μm. Furthermore, the splitting tensile strength showed a high healing performance when the capsule proportion mixed was 15% and its size was 850 μm. In the case of the permeability test, a capsule size of 850 μm showed a healing effect greater than 95%. Cracks with a width of up to 200 μm tended to heal using capsules with a size of 600 μm to 850 μm.

Solidified sludge, a potentially useful engineering material, contains organic matter that decomposes, releasing humic acid. The resultant corrosion reduces the compressive strength of the solidified sludge. This can be ameliorated by adding small quantities of lime and cement, which creates a strongly alkaline environment; unfortunately, the improvement is not long-lasting. We attempted to counteract this by adding metakaolin, which can capture calcium ions and form a stable binder in the solidified soil. The resulting material proved strongly resistant to the erosive effect of humic acid, improving and maintaining the durability throughout the curing period (180 days). [ABSTRACT FROM AUTHOR]

In this study, the method of changing the surface layer microstructure of cementitious composites by ultrasonic surface treatment at the early stage of hydration is introduced, and the formation mechanism of the gel phase powder layer (GPPL) formed by ultrasound is analyzed. The microstructure of GPPL is observed and analyzed by laser confocal microscopy scanning (LCMS), scanning electron microscopy (SEM) and backscattered electron (BSE) imaging. The phase component is measured by X-ray diffraction (XRD) and thermogravimetry (TG). Four ultrasonic frequencies (28, 40, 80, and 120 kHz) were used in the experiment. Apparent density and water vapor permeability of the cement paste specimens with GPPL structure were tested. The accelerated carbonation test of concrete and mortar specimens with GPPL structure were carried out. It is proved that GPPL structure can significantly improve the carbonation resistance performance of cementitious composites. Finally, the prospects for engineering applications of this method are presented. [ABSTRACT FROM AUTHOR]

In this paper, we take cement mortar and paste as specimens, a novelty method named ultrasonic surface treatment(UST) was employed to form a hardening surface layer on cementitious specimens to improve its wind-blown sand erosion resistance, surface hardness and apparent density. The specimens with curing ages of 1-day, 3-days, 7-days, and 28-days were adopted. The wind blown sand erosion test was carried out in a wind-blown sand erosion test system, which simulated a wind blown sand environment of a wind speed of 30 m/s and a sand feed rate of 30 g/min. The erosion angle of 30°, 60°, 90° were adopted. The mass loss in erosion process was measured, then the erosion resistance was calculated. The surface hardness was tested with a Vickers micro hardness tester. The apparent density of cement paste was measured with mass volume method. The data provided reveal the improvement on wind blown sand erosion resistance, surface hardnenss and apparent density of cementitious materials with ultrasonic surface treatment. That may be used in the investigation on improving the erosion resistance and to evaluate the effectiveness of the UST method on cementitious materials.

This work presents the effect of partially replacing metakaolin with Portland limestone cement to produce mortars for construction. Teleku Bokazo kaolin was explored as a SCM in the production of mortars. The hydration product between Portland limestone and metakaolin was studied. The kaolin was heat treated to form metakaolin and partially used to replace Portland limestone cement (PLC) in mortars to explore the optimum replacement and its mechanical and durability effect. The samples were characterized using X-ray diffraction (XRD) for phases and crystallinity of the kaolin. Fourier transform infrared spectroscopy (FTIR) and Scanning electron microscopy (SEM) gave information on the functional groups formed during the hydration and structure and surface morphology respectively. The pastes and mortars produced were subjected to setting time, water absorption, flexure and compression strength test. The mechanical properties were observed to increase with increasing metakaolin replacements. Therefore, from the results obtained, it is suggested that ∼20 % replacement of Portland limestone cement with Teleku Bokazzo metakaolin can be very suitable for construction applications.

Nitric oxide generated from various sources like car combustion is one of the most surrounding pollutants, which can be transferred from one form to another in the presence of sunlight. Titanium dioxide considered one of the most environmentally friendly active photocatalytics that can be used with building materials safely and effectively to react with nitric oxides. To study the possibility for the reduction of air pollutants like nitric oxides, two types of substrates coatings were prepared. First, mixing nano particles of TiO2 with cement paste in two percents 3% and 6%. Second, mortar substrates coated with nano TiO2 aqueous solution. Two coating methods have been used dip and spray. A laboratory test procedure was adopted to assess the performance of the prepared photoactive specimens. The specimens were subjected to NO gas and there efficiency in gas removal was monitored with time. Results showed the effectivity of coating building materials with titanium dioxide, the removal of gaseous pollutants like nitric oxide reached to 98.85% when spray and dip methods are used. Mixing nano titanium with a percent of 3% was also efficient in the removal of nitric oxides, the removal reached to 97%. It was concluded that spray method was more practical to be used.

Titanuim dioxide represents a novel photocatalyst material that can be used in different ways for air pollutants remediation. Air pollutants that are spreaded in the surrounding air could be transferred to more complex materials, especially in the presence of sunlight. To study the possibility for the reduction of these pollutants a laboratory tests have been conducted on the coated specimen substrate by using nitric oxide as pollutant gas, and there efficiency in gas removal was monitored with time. Two different particle sizes of TiO2 have been used; micro with particle size range between 150-200 nm and nano PC105 with particle size 20+ 5 nm, both are 100% anatse. Two coatings methods were applied on cementitious substrate material dip and spray to study the photochemical reaction with TiO2, aqueous solution prepared by dispersing 3g/L of TiO2 with deionized water and ethanol. Results show that using nano and micro size TiO2 aqueous solutions were effective in the removal of nitric oxidewith variations in the time consumed for the removal. Using nano aqueous solution in both dip and spray methods gives the same removal efficiency reached to 98.85% ,while using micro aqueous solution the removal reached to 98.08% when dip method was used and 87.69% when spray method was used.

Pumice stone is a natural sponge-like lightweight aggregate formed during the rapid cooling and solidification of molten lava. After suitable preparation, it can be used as an aggregate to produce lightweight concrete or as a cementitious material to produce blended cement or geopolymer. This article focused on the influence of pumice powder (PP) on fresh properties and hardened properties of conventional cementitious materials and geopolymers. Additionally, different modification methods carried out to modify some properties of conventional cementitious materials containing PP have been included. This review showed that the incorporation of PP in the traditional cement matrix has some benefits such as increasing thermal and acoustic insulation, increasing fire resistance, increasing abrasion resistance, decreasing unit weight, decreasing hydration heat, decreasing drying shrinkage, decreasing autoclave expansion, increasing sulfate resistance, increasing seawater resistance, increasing acid resistance, increasing electrical resistivity, decreasing alkali silica reaction (ASR) expansion, decreasing porosity, water absorption and permeability. On the other hand, it has a negative effect on workability, mechanical strength and increasing carbonation rate. This review also confirmed that PP has a promising future in the field of alkali-activated and geopolymer materials. [ABSTRACT FROM AUTHOR]

This paper focuses on the comparison of experimentally obtained data with the shrinkage model B4 designed by a research group led by Professor Z. P. Bažant. Two cementitious materials, one having a high water-cement ratio (w/c) and one having a low w/c, were prepared for the experiment. Intentionally, the test specimens were not protected from drying during the entire period of measurement. Test results confirmed that the actual shrinkage process as measured does not correspond with the prediction model, especially during its early age. Shrinkage during the plastic and semi-plastic stages of the solidification process is not reflected in the predicted shrinkage curve. However, if the start time of the evaluation of the experimental data corresponds to the time of maximum derivatives of the temperature, length changes, and ultrasonic pulse velocity curves, better correspondence between the experiment and prediction model is observed for material with a low w/c. However, this approach does not improve the correspondence between the experiment and numerical prediction in the case of material with a high w/c. [ABSTRACT FROM AUTHOR]

In this research high speed milling was carried out on particles of brown coal raw fly ash, on second layer, and on third layer particles obtained from wet separation of brown coal raw fly ash. Due to milling process, median particle size d50 of raw fly ash, second layer, and third layer reduced by 46%, 23%, and 77%, densities reduced by 11%, 17%, and 8% respectively. Due to milling process, formation of agglomerations was observed, the standard deviation of the chemical composition of each element from the mean value reduced. After milling, high volume cementitious paste mixes were prepared with 60% cement replacement. Due to the milling process the increase in compressive strength at 28 and 90 days was observed for raw fly ash is 59% and 16%, for second layer is 12% and 15%, for third layer and milled third layer is 78% and 75%. Flexural strength testing showed that due to the milling process the deflections at maximum loads have reduced considerably leading to brittle behavior of milled cementitious specimens. The testing for Mercury Intrusion Porosimetry showed that the cementitious specimens of third layer have maximum concentration of large capillary pores between 0.05 and 10 µm, whereas, all others have maximum concentration of medium capillary pores between 0.01 and 0.05 µm. Autogenous shrinkage of cementitious specimens was measured for first sixteen hours after mixing which showed that the second layer particles have the least shrinkage as compared to all other specimens. [ABSTRACT FROM AUTHOR]

Highlights • Increase in reinforcing effect of graphene oxide at strain rate up to 1700 s−1. • Graphene oxide increases DIF when the strain rate reaches different thresholds. • Correlation is found between the increase in DIF and the speed of crack development. Abstract The reinforcing effect of graphene oxide on cementitious materials under high strain rate remains largely unknown. Existing studies on microfiber reinforced cementitious composites showed that the dynamic increase factor (DIF) decreases due to these fibres. This study reports that the reinforcing effect of graphene oxide nanosheets can, in contrast, increase with strain rate. Tensile splitting and compression tests were conducted under both static and dynamic loadings. High strain rate, up to 1700 s−1, is achieved using a split Hopkinson pressure bar apparatus. It is found that the DIF of graphene oxide nanocomposite only increase when the DIF is higher than a threshold which is about 780 and 30 s−1 for compression and tensile test respectively. The increased of DIF was correlated with the speed of crack development and pull-out of the graphene oxide nanosheets. Also, the pull-out or fracture of graphene oxide on fragmented sand was also found a possible contributing factor to the increased DIF. The findings of this study indicate the future potential of atomic-thin nanosheets for materials under extreme impact and blast loading. [ABSTRACT FROM AUTHOR]

For years, supplementary cementitious materials (SCM) has been extensively used as an integral component in the production of concrete. This has been motivated by sustainability efforts and reduced environmental impact. Correspondingly, this study intended to develop an appropriate method for the use of rice husk ash (RHA), a by-product of rice husk (RH) which exists abundantly in the Philippines, as a partial replacement to ordinary Portland cement (OPC). Different studies have suggested optimal percentage replacement values of RHA, from 10% to 20%, which demonstrated vast improvement in strength of the resulting blended concrete. These optimal values, however, immensely depends on the burning preparation of RHA which adversely affects the amorphous silica components, and therefore the pozzolanic activities of RHA in concrete. In this research, a potential approach to convert RH into optimized and highly reactive RHA by controlled burning and grinding is provided. The effect of RHA in the strength of cement mortar was investigated through the various proportions of 5, 10, 15, and 20% RHA by weight replacement of cement. Some of the findings are: (i) controlled combustion of RH with temperature ranging from 400 to 600 °C and a slow method of cooling for 6 to 8 hours were some of the critical factors needed to produce high silica content, (ii) concrete containing up to 10% RHA replacement is optimal in maximizing the strength of cement mortar, and (iii) the incorporation of RHA in concrete by 15% and 20% replacement by weight indicated a lower workability. [ABSTRACT FROM AUTHOR]

The study examined the durability properties of concrete added with Nano-silica. Lifeline buildings and other infrastructures have highlighted concrete durability issues. The use of nanoparticles in materials based on cement has been recently attractive because of the unique properties at Nano-level that they are able to achieve. This can be prominently utilized in enhancing the ductility of cement-based composites which are generally brittle, also cracks at the nanoscale could be arrested by incorporating carbon nanotube or carbon nanofiber. Nano-silica has a unique advantage in the potential pozzolanic-reaction with cement hydration products over other nanoparticles. Addition of Nano-silica is known to redefine pore size and distribution which would alter the durability of the concrete. Durability properties were tested by checking how concrete of grade M30, with 2% by weight of its cementitious materials replaced with Nano-silica, withstands in alkali environment, acidic environment, sulphate environment, and in a water curing in comparison to conventional concrete of M30 grade in respective environments. The Nanofiller effect and the pozzolanic-reaction increased the homogeneity of the microstructure and the porosity, particularly at the Interfacial Transition Zone, which decreased the permeability of deteriorating gases. Durability tests validated the positive effects of Nano-silica added to concrete. The distribution of pore size also showed that Nano-silica refined the large capillary pores, subsequently decreasing the permeability nature of concrete, enhancing its durability. Also, Nano-silica added concrete mix shows increased compression strength, tensile strength, and flexural strength compared to the conventional concrete mix. [ABSTRACT FROM AUTHOR]

This study aims to examine the potential use of a geopolymeric matrix as a sustainable alternative to commercial mortars in carbon fabric-reinforced matrix composites. Single-lap shear tests were conducted to examine the bond behavior at the fabric-matrix interface. Test parameters included the type of matrix (geopolymeric and cementitious matrices) and the bonded length (50 to 300 mm). The geopolymeric matrix was a blend of fly ash/ground granulated blast furnace slag activated by an alkaline solution of sodium silicate and sodium hydroxide. The bond behavior of the geopolymeric-matrix specimens was characterized and compared to that of similar specimens with a cementitious matrix. The specimens failed due to fabric slippage/debonding at the fabric-matrix interface or fabric rupture. The effective bond lengths of the geopolymeric- and cementitious-matrix specimens were 150 and 170 mm, respectively. The geopolymeric-matrix specimens exhibited higher fabric strains, higher ultimate loads, and a steeper strain profile along the bonded length than those of their cementitious-matrix counterparts. New bond-slip models that characterize the bond behavior at the fabric-matrix interface for geopolymeric- and cementitious-matrix specimens were developed. Both models exhibited equal maximum shear stress of 1.2 MPa. The geopolymeric-matrix model had, however, higher fracture energy and higher slip at maximum shear stress than those of the cementitious matrix model.

The debonding behavior of natural fibers with cement matrix at elevated temperatures has been investigated by introducing a new test method for measuring the interfacial shear strength between the fibers and the cement matrix in the field of cementitious composites research. In addition, the effects of shrinkage, surface roughness, and tensile strength changes of natural fibers on the interface at high temperatures were analyzed by characterizing the failure process of chemical bonding with the matrix due to changes in the surface functional groups of natural fibers. The results show that the bonding properties between natural fibers and the cement matrix gradually decrease with increasing temperature, which is due to the contraction of the natural fibers in the radial direction at high temperatures leading to debonding with the cement matrix on the one hand, and the degradation of chemical bonding enhancement due to the reduction of polar groups on the surface of the fibers on the other hand, which contributes to the reduction of the interfacial strength between the fibers and the matrix. In the post-high-temperature phase, the temperature dependence of the inherent material properties of the natural fibers leads to a decrease in the mechanical properties as an additional factor affecting the interfacial behavior. This work evaluates the durability of natural fibers in cement matrices under high temperature conditions from the viewpoint of their inherent physical properties and surface chemical properties, providing unique research ideas and insights for related studies. Meanwhile, a new experimental method is introduced in the field of fiber-reinforced cementitious composites interface research, which can be widely attempted to be used in the study of selective combinations of different fiber-matrix interfaces, fiber size selection, and fiber modification to optimize the overall performance of the composites, which is of great significance to the research in this field. • The bonding properties between FCNTs repair mortar and fire exposed old mortar substrate has been investigated. • The bonding strength and microscopic test were performed to determine the mechanism of FCNTs in the ITZ. • An effective prediction model is proposed to quantify the effects of porosity and different FCNTs. [ABSTRACT FROM AUTHOR]