Partial Replacement Of Portland Cement Research Articles

Sulfate activation of wheat straw ash to enhance the properties of high-performance concrete with recycled aggregates and waste tire steel fibers.

A sustainable alternative to conventional concrete involves using recycled aggregates (RA) instead of natural aggregates (NA) and incorporating wheat straw ash (WSA) as a partial replacement for Portland cement. The demand for high-performance concrete (HPC) is rising due to the need for architecturally complex structures and long-span bridges, but HPC's low ductility necessitates reinforcement. Waste tire steel fibers (WTSFs) are gaining popularity for their tensile strength. However, WSA-RA concrete's low early strength is a challenge. Chemical activators like sodium sulfate can enhance early-age strength. This study evaluated the durability and strength of fiber-reinforced concrete with both inactivated and activated WSA. Tests included compressive strength, indirect tensile strength, modulus of rupture (MOR), acid attack resistance, chloride penetration, sorptivity, and water absorption. Activated WSA-RA concrete showed significantly improved early strength. The mixture with 30% RA, 40% WSA, WTSFs, and activator exhibited the highest strength at 90 days. At 60% RA content, activated concrete with 40% WSA and 2.5% WTSFs outperformed the control. Durability was enhanced with a 14-17% reduction in water absorption and sorptivity and a 25.2% decrease in chloride penetration. Acid resistance improved by 26%. X-ray diffraction (XRD) confirmed these findings with elevated hydration product peaks. This study demonstrates that chemical activation of WSA optimizes the engineering properties of WSA-modified HPC with WTSFs and RA, providing a sustainable solution to their challenges.

Effects of bamboo leaf ashes on concrete compressive strength, water absorption, and chloride penetration

Bamboo leaves are an agro-waste from the bamboo industry that carries a significant environmental impact, primarily due to its phytotoxic activity. In this paper the pozzolanic potential of bamboo leaf ashes are assessed. Bamboo leaves were calcined at five different temperatures - 500, 600, 700, 900, and 1000 °C. The obtained ashes were characterized using X-ray diffraction, X-ray fluorescence, differential thermal gravimetric analysis, Modified Chapelle's method, and Pozzolanic Activity Index. The ash calcined at 600 °C, exhibiting the highest pozzolanic activity, was used in concrete production as a partial replacement for Portland cement at levels of 5 %, 10 %, and 15 %. Concrete compressive strength, water absorption, and chloride diffusivity were assessed. The results indicate that the use of BLA significantly improves the concrete performance, increasing 28-day compressive strength by up to 18 % and reducing the non-steady state chloride penetration by up to 71.2 %. Overall, the use of bamboo leaf ashes obtained at 600 °C leads to significant improvements in mechanical and durability-related properties of concrete, indicating the viability of using this agro-waste as a supplementary cementitious material.

Developing greener concretes from spent bleaching earth and sugarcane bagasse ash

Concrete is by far the most widely utilized construction material due to its excellent mechanical and durability properties. However, the concrete industries are notorious for their anthropogenic activities that contribute to climate change. Cement production alone consumes immense amounts of energy and trails a significant CO2 footprint. One solution that researchers have deemed promising over the last couple of decades is the substitution of cement with agricultural waste products, which subsequently serves to alleviate waste disposal problems. This study investigates the suitability of spent bleaching earth (SBE) and sugarcane bagasse ash (SCBA) as partial replacement of ordinary Portland cement (OPC) in increments of 0, 5, 10 and 15% by mass. Tests were conducted in accordance to British Standards to assess the consistence, compressive strength, split tensile strength and drying shrinkage strain of SBE and SCBA based concretes. Results indicated that while these concretes displayed similar degrees of consistency, the SCBA concretes exhibited superior compressive and tensile strengths. Optimum SCBA dosages were revealed to be about 5-10%, yielding a 7-12% and 3-8% increase in compressive and tensile strengths, respectively, as compared to OPC concrete. Drying shrinkage behavior was also improved in the SCBA concretes. Further, comparisons of the mechanical and durability performances of the concretes with British and American codes suggest that up to 10% replacement of cement with SCBA may be a viable approach to developing sustainable materials for the concrete industry.

Influence of replacing Portland cement with anionic asphalt emulsion on vibration damping, mechanical and microstructural properties of concrete

The effect of anionic asphalt emulsion (AE) as partial replacement of Portland cement to enhance the damping properties of concrete was examined. Five concrete mixtures were designed and prepared, increasing AE content from 0 to 40% in overall binder volume, in 10% increments. Loss factor, dynamic moduli, resonant frequencies, and compressive strength were obtained at the age of 7, 28, 90, and 180 days. Results show that the loss factor of concrete increased as the asphalt content increased, whereas the dynamic modulus and resonant frequency decreased. In addition to the viscous damping contributed by asphalt droplets, the more porous microstructure and weaker interfacial transition zones in AE modified concrete can also enhance the damping properties. However, an inverse correlation between concrete strength and damping can be observed with increasing AE content, where the substitution of AE results in a significant decrease in the compressive strength of concrete. Therefore, the anionic AE modified concrete seems to be more suitable for non-structural application where strength is not a key requirement.

The influence of sugarcane bagasse ash on the microstructure of autoclaved cementitious material: Comparative study with amorphous and crystalline silica

This study aimed to investigate the effects of a partial replacement (25 wt%) of Portland cement with sugarcane bagasse ash (SCBA) on the microstructure of cement pastes. The effects were compared with those of pastes containing amorphous (silica fume) or crystalline (crushed quartz) silica. Two curing methods were used for the pastes: conventional curing (25 °C and RH > 95%) and autoclave curing (220 °C under 2.1 MPa for 8 h). The microstructure of the pastes was characterized by XRD, SEM, FTIR, and the hardness and elastic modulus of their C–S–H regions. The results showed that the pastes cured at room temperature exhibited similar microstructure development, showing little or no reaction, even though silica fume is a highly reactive pozzolanic material. Differently, the hardness of the pastes containing silica fume, SBCA and crushed quartz replacement for cement increased approximately threefold after autoclave curing, while, in contrast, the reference sample, no cement replacement, showed no improvement. This is attributed to the formation of tobermorite and xonotlite. The presence of Al in the SCBA allowed the formation of tobermorite under the autoclave curing conditions (220 °C, 2.1 MPa for 8 h), and in this case, the SCBA exhibited behavior between silica fume and fine quartz.

Robust prediction models for flow and compressive strength of sustainable cement grouts for grouted macadam pavement using RSM

This study investigates the utilization of pumice stone ash in cementitious grouts for grouted macadam pavement, aiming to enhance flowability and compressive strength. Partial replacement of ordinary Portland cement (OPC) with varying percentages (5–20 %) of powdered pumice stone (PPS) ash was explored, alongside adjustments in water-to-cement (w/c) ratios. Experimental assessments, including flowability tests and compressive strength evaluations, were conducted on fresh and hardened grouts. Response surface methodology (RSM) and ANOVA analysis were employed to analyze the relationship between pumice stone ash content, w/c ratio, flow, and compressive strength. The results show that increasing the PPS content from 0 % to 20 % led to an increase in flow time from 23.6 to 34 seconds at a 0.3 w/c ratio, from 9 to 19 seconds at a 0.35 w/c ratio, and from 7 to 14 seconds at a 0.40 w/c ratio: indicating reduced flowability of the grouts. The 7-day compressive strength increased by approximately 2–17 % when 5–15 % of the cement was replaced with PPS, but a reduction occurred at 20 % PPS. Similarly, the 28-day compressive strength increased by about 4–23 % with 5–15 % PPS, while 20 % PPS led to a decrease in strength. The results highlight specific combinations of pumice stone ash content and w/c ratios, particularly 10 % PPS at 0.35 w/c and 15 % PPS at both 0.35 and 0.40 w/c, that meet grouted macadam standards, balancing flowability and strength. Fit statistics demonstrate the reliability of the predictive model. Optimization aims to maximize pumice stone ash content and w/c ratio, with graphical representation indicating an optimal composition at 17.25 % PPS and 0.35 w/c ratio for efficient grouted macadam construction. Additionally, Significant contribution towards sustainability can be achieved by replacing cement with pumice stone ash in pavement construction.

Geothermal Nano-SiO2 Waste as a Supplementary Cementitious Material for Concrete Exposed at High Critical Temperatures.

The partial replacement effect of Portland cement by geothermal nano-SiO2 waste (GNSW) for sustainable Portland-cement-based concrete was investigated to improve the properties of concrete exposed at high critical temperatures. Portland cement was partially replaced by 20 and 30 wt.% of GNSW. The partial replacement effect on Portland-cement-based concrete subjected to 350, 550, and 750 °C was evaluated by measuring the weight changes, ultrasonic pulse velocity, thermogravimetric and differential thermal analysis, X-ray diffraction, surface inspection, and scanning electron microscopy under residual conditions. The ultrasonic pulse velocity results showed that the GNSW specimens maintained suitable stability after being heated to 350 °C. The SEM analysis revealed a denser microstructure for the 20 wt.% of partial replacement of Portland cement by GNSW specimen compared to the reference concrete when exposed to temperatures up to 400 °C, maintaining stability in its microstructure. The weight losses were higher for the specimens with partial replacements of GNSW than the reference concrete at 550 °C, which can be attributed to the pozzolanic activity presented by the GNSW, which increases the amounts of CSH gel, leading to a much denser cementitious matrix, causing a higher weight loss compared to the reference concrete. GNSW is a viable supplementary cementitious material, enhancing thermal properties up to 400 °C due to its high pozzolanic activity and filler effect while offering environmental benefits by reducing industrial waste.

Exploring the effect of self-combustion gangue powder particle distribution on rheological behavior and hydration mechanism in cement-based systems

Solid waste-based mineral admixtures are widely employed as a partial replacement for Portland cement due to their superior performance and minimal carbon and environmental footprint. This study involves the production of self-combustion gangue powder (SCGP) with varying particle sizes achieved through crushing, screening, and grinding. The SCGP is subsequently blended with cement to form a self-combustion gangue powder-cement (SCGP-C) system with diverse particle size distribution. Rheological tests and hydration exothermic tests were conducted to investigate the rheological behavior and degree of hydration of the SCGP-C mixed system. The results show that SCGP enhances the plastic viscosity and thixotropy of the mixed slurry. However, when a finer SCGP (d50=1.36 μm) was used to replace 15 % of the cement for the same mass, the yield stress and rheological index of the slurry were reduced by 28.1 % and 15.4 % respectively compared to the control group, while the closed-packing of the SCGP-C system was obtained. When the cement was replaced by 15 % SCGP (mass substitution), the yield stresses of finer and coarser SCGP (d50=18.24 μm) and pure cement slurries were increased by 289.1 %, 67.3 %, and 29.2 %, respectively, at T=60 min compared to T=0 min. This suggests that the fineness of SCGP has a greater effect on the yield stresses of mixed slurries over time. Mixed slurries with different finenesses of SCGP all prolonged the hydration induction period and reduced the total exothermic heat of hydration. Incorporating 15 % finer SCGP extended the induction period of the mixed slurry by 27 min and increased the peak value of the main hydration curve. Appropriate incorporation of SCGP helps to improve the fluidity and early strength of mortar in the SCGP-C system and promotes the physical filling effect and the positive role of SCGP volcanic ash in the cement system.

Determination of Fracture Mechanic Parameters of Concretes Based on Cement Matrix Enhanced by Fly Ash and Nano-Silica.

This study presents test results and deep discussion regarding measurements of the fracture toughness of new concrete composites based on ternary blended cements (TCs). A composition of the most commonly used mineral additive (i.e., fly ash (FA)) in combination with nano-silica (NS) has been proposed as a partial replacement of the ordinary Portland cement (OPC) binder. The novelty of this article is related to the fact that ordinary concretes with FA + NS additives are most often used in construction practice, and there is a decided lack of fracture toughness test results concerning these materials. Therefore, in order to fill this gap in the literature, an extensive evaluation of the fracture mechanic parameters of TC was carried out. Four series of concretes were created, one of which was the reference concrete (REF), and the remaining three were TCs. The effect of a constant content of 5% NS and various FA contents, such as 0, 15%, and 25% wt., as a partial replacement of cement was studied. The parameters of the linear and nonlinear fracture mechanics were analyzed in this study (i.e., the critical stress intensity factor (KIcS), critical crack tip opening displacement (CTODc), and critical unit work of failure (JIc)). In addition, the main mechanical parameters (i.e., the compressive strength (fcm) and splitting tensile strength (fctm)) were evaluated. Based on the studies, it was found that the addition of 5% NS without FA increased the strength and fracture parameters of the concrete by approximately 20%. On the other hand, supplementing the composition of the binder with 5% NS in combination with the 15% FA additive caused an increase in all mechanical parameters by approximately another 20%. However, an increase in the FA content in the concrete mix of another 10% caused a smaller increase in all analyzed factors (i.e., by approximately 10%) compared with a composite with the addition of the NS modifier only. In addition, from an ecological point of view, by utilizing fine waste FA particles combined with extremely fine particles of NS to produce ordinary concretes, the demand for OPC can be reduced, thereby lowering CO2 emissions. Hence, the findings of this research hold practical importance for the future application of such materials in the development of green concretes.

Effect of silica fume on the microstructural and mechanical properties of concrete made with 100% recycled aggregates

Recycled concrete aggregate can be utilized in structural concrete in order to reduce the use of natural resources and the harmful impacts of waste concrete on the environment. This present research aimed to assess the effectiveness of using recycled aggregate concrete with the partial replacement of cement by silica fume (SF) to analyze the microstructural and mechanical properties of recycled aggregate concrete (RAC). In this study, recycled stone was used as coarse aggregate. The main variables of the study included the dosage of silica fume that was employed as a partial replacement of ordinary Portland cement (OPC) with four different percentages: 4%, 8%, 12%, and 16% by weight. Five different mixes were prepared, with four mixes created by varying amounts of silica fume, which were designated as RSACSF4, RSACSF8, RSACSF12, and RSACSF16. The other mix was created as a reference mix without silica fume and designated RSACSF0. Slump test was conducted to investigate the workability of concrete mixes. From the test result, a decreasing trend was found after adding more percentage of SF. Compressive and splitting tensile tests were conducted to analyze the mechanical properties of RSAC at 7 and 28 days. The results showed that the addition of SF improved the performance of RSAC at early and later curing ages, and a 12% addition of SF showed the best result. Scanning electron microscopy and X-ray diffraction analysis were performed to explore SF's microstructural performance and effect on RSAC. The results showed that silica fume showed a positive pozzolanic impact, and when combined with calcium hydroxide, it underwent a secondary hydration reaction that boosted the generation of calcium silicate hydrate and improved the parameters of the interface transition zone. X-ray diffraction analysis showed that silica fume and silica fume have similar pattern intensities. Finally, 12% SF is recommended as a partial replacement for cement in RSAC.

Compressive Strength Study on Reactive Powder Concrete with 30% Quartz Sand and Variations in Fly Ash Composition as Partial Substitution of Cement

The concrete industry is considered environmentally unfriendly and unsustainable due to the significant consumption of natural materials. Currently, the industry predominantly uses Portland cement as its main ingredient, leading to an increase in Portland cement production. However, the use of fly ash can help make the concrete industry more sustainable in the future. Fly ash can be used as a partial replacement for Portland cement in concrete production. This study aims to determine the effect of fly ash variations on the compressive strength of reactive powder concrete. The research method used is experimental. The concrete mix design includes 30% quartz sand and fly ash variations of 0%, 5%, 10%, 15%, 20%, and 25%. The compressive strength test specimens are cylindrical with a diameter of 7.5 cm and a height of 15 cm. The resulting test specimens have a compressive strength of more than 41.4 MPa, thus qualifying as high-strength concrete. The compressive strength test results for fly ash variations of 0%, 5%, 10%, 15%, 20%, and 25% are 62.62 MPa, 66.27 MPa, 75.59 MPa, 68.78 MPa, 66.21 MPa, and 63.70 MPa, respectively.

Innovative utilization of agro-industrial by-products: Bamboo leaf ash as a pozzolanic material for extruded fiber cement composites

This study aims to promote the valorization of agro-industrial waste and sustainability in the construction industry by evaluating the potential of bamboo leaf ash (BLA) as a partial replacement for Portland cement in extruded fiber cement. Squeeze flow, physical, mechanical, and microstructural analyses (Scanning Electron Microscopy and X-ray microtomography) were conducted. The results showed that the incorporation of fibers and BLA leads to an increased water demand and, consequently, an increase in porosity and pore connectivity. However, the mix design with 10 % replacement exhibited improved mechanical behavior for modulus of rupture (10.2 %) and limit of proportionality (4.5 %), when compared to a formulation without BLA. For the other parameters, the mix design with 10 % BLA showed mechanical behavior with no statical difference to the mix design without ash. Thus, the use of BLA as a partial replacement for Portland cement represents an alternative with technical and environmental improvements for fiber cement.

Hydration, phase assemblage and microstructure of cementitious blends with low-grade limestone

Limestone of the purity mandated by the standards for use in cement manufacture (as raw material or as performance improver) is only a fraction of the mined material. Sometimes, limestone contains impurities like silica, clay, dolomite etc. beyond the levels specified for use as an additive or for cement production. This limestone, commonly known as low-grade limestone, also may have a potential to be used as a supplementary cementitious material. This paper reports a study conducted to understand the hydration behaviour of ordinary Portland cement in combination with low-grade limestone. Low-grade limestone samples with dolomite, silica and clay impurities were collected from various limestone mines in India and used in cementitious blends at various replacement levels after suitable processing. Reaction kinetics was studied using calorimetry and phase assemblage using techniques like X-ray diffraction and thermogravimetry. Mercury intrusion porosimetry was employed to study the microstructure of cementitious blends. Dilution effect of low-grade limestone was studied by measuring compressive strength of cement mortar cubes for various replacement levels. Shortening of induction period, increased peak heat rate and reduced time to peak were observed in the blends of ordinary Portland cement with low-grade limestone. Carboaluminate formation, ettringite stabilisation and higher bound water content were also seen. The studies showed that low-grade limestone also can be used as a partial replacement for ordinary Portland cement without compromising the strength up to 15% replacement. Higher replacement levels, although showing a reduction in strength due to dilution effect, could still be considered for non-structural applications.

Recycling Possibilities of Wood-Cement Particle Board Manufacturing Waste

Wood-cement particle boards are gaining popularity within construction materials as they combine natural fiber architectural value with Portland cement durability. The production of the material is associated with processing the produced fiberboards, which includes cutting, grinding, and polishing. The remaining wood-cement dust residues are classified as production waste, which is now deposited in the dump and gives extra expenditure for the enterprise. The utilization of wood-cement dust would also benefit the circular economy and reduce the environmental impact of the production process. Two scenarios are analyzed in this research, and the life cycle assessment (LCA) tool with SimaPro software is compared. The first scenario is associated with the partial replacement of Portland cement with wood-cement dust powder. The second scenario offers re-activation of the wood-cement dust at 450 °C to obtain binder properties. Both materials' mechanical strength is comparable, reaching 10 MPa after 28d curing. To maintain target strength, 70 % of Portland cement can be replaced. To produce 1 t of binder by heating at 450 °C, 1.2 t of wood-cement dust is needed as natural moisture evaporates, and wood dust particles go through pyrolysis, giving extra heat and CO2 emissions as well. LCA results indicate the 70% replacement of Portland cement reduces CO2 emissions from 597 kg of CO2/ton of CEM II/A-LL 42,5 to 179 kg of CO2/ton, while the second scenario is associated with high energy consumption during burning of the binder and increased CO2 value due to fossil fuel consumption and CO2 release from burning organic compounds in the material.

Characteristic evaluation and environmental validation of self-compacting concrete containing sandstone slurry waste for sustainable usage.

This study aims to understand the impact of concrete ingredients on the environment. To analyze the effect of, three significant indexes have been taken into consideration, which are embodied carbon dioxide index (e-CO2), embodied energy consumption (e-energy), and embodied resource consumption (e-resource) index. The life cycle assessment (LCA) methodology has considered veto comprehending the probable application of sandstone waste in the form of a slurry (Sslurry) and powder (Spowder) for the development of self-compacting concrete (SCC). This study can be proven beneficial to evaluate the potential adverse effects from environmental and energy perspectives. One reference mix and eighteen design mixes of SCC have been designed and developed to perform an experimental program. An environmental impact comparison of the "hybrid" SCC was performed using the OpenLCA life cycle analysis software with Ecoinvent LCIA methods. The outcomes of this experimental program reveal that the partial replacement of pozzolana Portland cement (PPC) with Sslurry can reduce e-CO2 emission along with the e-energy and e-resource parameters. When Spowder was used as the partial substitution of fine aggregate (FA), only the e-resource index decreased, and e-CO2 and e-energy increased. Minimalist impact on the environment has been noticed when SCC is prepared with Sslurry and Spowder. A detailed LCA analysis study justifies the utilization of Sslurry and Spowder in SCC, which exhibits encouraging results concerning strength and quality. Hence, it was observed that Sslurry and Spowder in developing green and sustainable SCC with moderate strength characteristics are beneficial from an environmental impact perspective.

Pozzolanic activity of FCC catalyst waste slag (CWS) for cement and geopolymer production

Catalyst waste slag (CWS) is generated in large amounts when fabricating the catalyst required in the fluid cracking catalyst (FCC) process used for oil refining. Currently, CWS is landfilled. This paper characterizes the CWS and measures its pozzolanic activity. It determines whether the CWS can be used as partial Portland cement (PC) replacement for the first time in the literature. CWS is primarily composed of Al2O3 and CaO. It contains a negligible quantity of heavy metals that can be immobilised in a matrix. The raw CWS is totally amorphous and extremely reactive which results in flash set. Calcination is an effective method to control the reactivity of CWS. Reactivity increased when CWS was calcined between 300 and 600 °C and it peaked at 500 °C, but this caused flash set. Calcination at 800 °C lowers reactivity (as the highly disordered aluminium phases achieve a greater order) which allows for proper handling. Temperatures over 800 °C caused partial crystallization significantly lowering reactivity.The 800°C-calcined CWS reached high mechanical index (6.25), comparable to other pozzolans such as fly ash and red mud, and greater than alum sludge. CWS combines lime profusely and develops more abundant cementing hydrates than similar pozzolans such as calcined alum sludge. The pozzolanic reaction of the 800°C-calcined CWS provides abundant cementing minerals including AFt and AFm phases, calcium aluminium carbonate hydrates and calcium aluminium hydrates.The high reactivity of CWS and its prolific production of cementing phases in pozzolanic reactions indicate that it can be used as a supplementary cementitious material in PC and lime systems; and that it can be used as a precursor to produce low-carbon and geopolymer cements. CWS constitutes a reactive aluminium source which, in a PC system, participates in hydration reactions and can enhance the properties of the resultant materials.

Durability and ecological assessment of low-carbon high-strength concrete with short AR-glass fibers: Effects of high-volume of solid waste materials

The goal of this research is to improve the mechanical characteristics and durability of concrete while adhering to green and sustainable development principles. Portland cement (PC) was replaced with ceramic waste powder (CWP), glass powder (GP), and granite waste powder (GWP) to create the low-carbon, high-strength concrete (HSC). These materials were incorporated at 0–50% as a partial replacement of PC. The short alkali-resistant (AR-) glass fiber content was added by 1.0% of the PC content. The changes in strength, microstructure, pore structure, as well as ecological assessment of HSCs was investigated. Various experiments on the durability properties and elevated temperature resistance of HSC were performed. The experimental results show that mechanical properties of HSC with 10%GP and 20%GWP were maximally enhanced at 28d, while the mechanical properties of HSC with 50% of all wastes are decreased. It was found also that HSC containing CWP showed significant reductions in carbonation depth (up to 65.89% lower than the control mixture), especially at higher replacement levels. Furthermore, the increment in substitution level of CWP has found an increment in pore volume, resulting in a reduction in preliminary strength performance. It was observed that a 50% substitution level of GP and GWP reduced the water penetration depth by 47.71% and 65.7% compared to the control mixture, respectively. The residual strength after 600 °C exposure for 10%CWP, 10% GP, and 20% GWP retained about 34.10%, 32.32%, and 43.29%, respectively, from their original strength. XRD tests and SEM micrographs showed that adding 10%GP and 20%GWP improve the hydration reactions. Finally, environmental assessments revealed that incorporating CWP, GP, and GWP into HSC led to reduced costs, energy consumption, and carbon footprint.

Evaluating the Use of Recycled Brick Powder as a Partial Replacement for Portland Cement in Concrete

Portland cement is one of the most used construction materials. However, its production represents between 5 and 7% of the total CO2 emissions. On the other hand, during construction and demolition activities, different wastes are produced, including recycled brick powder (RBP), whose potential as a supplementary cementitious material (SCM) has been demonstrated in the literature. This research aims to evaluate RBP as a partial replacement for Portland cement in concrete. 5 to 10% of Portland cement was replaced with RBP in two strength designs (20 and 25 MPa) in order to propose concretes that meet the requirements for use in construction. Tests involving slump, compressive strength, tensile strength by diametrical compression, absorption, density, and void content were performed. The results show that a 5% RBP replacement does not affect workability in concrete mixes, as it maintains their mechanical resistance and slightly improves their physical properties. On the other hand, 10% RBP replacements adversely affect workability and reduce tensile strength. These results are attributed to pozzolanic activity and the physical effect caused by RBP, whose performance may be improved by reducing RBP particles and increasing their specific surface area (SSA). Using RBP as a replacement for Portland cement to produce concrete is a viable alternative with a sustainable approach.

Calcined schist as promising ordinary Portland cement substitution: C3

AbstractAn effective method to make cement and concrete more sustainable is to blend them with the proper supplementary cementitious materials (SCMs). This study evaluates a pair of schist‐type materials with slightly different phase compositions, as a partial replacement for ordinary Portland cement (OPC). Materials received from several mines in ground powder form were studied by X‐ray diffraction, thermogravimetric analysis (TGA), and scanning electron microscopy. According to the TGA results, the activation procedures for the candidate SCMs were determined. The as‐received powders were heat treated in three different decomposition regimes (30%, 50%, and 80% of the total weight losses during thermal decomposition). These regimes corresponded to the activation level of the potential SCMs due to the de‐hydroxylation of the clay‐type minerals within them. Pozzolanic reactivity (pozzolanicity) of untreated as well as treated powders were estimated via electrical conductivity measurements in saturated calcium hydroxide solution. Blended cement pastes with 30 wt.% of OPC substituted with calcined clay‐type materials have developed mechanical properties equal to those of pure cement (100 wt.% OPC) paste after 28 days of hydration time. Two blended cement pastes prepared with candidate SCMs were compared to 100% OPC and OPC composite paste with metakaolin, which is regarded in the literature as a standard.

Rice husk and snail shell ash as partial replacement of ordinary Portland cement in concrete – A review

This paper examines studies on the use of rice husk ash (RHA) and snail shell ash (SSA) as partial Ordinary Portland cement (OPC) replacements in concrete and their effects on concrete properties. RHA contains over 80% amorphous silica, along with other oxides in small quantities. Scanning electron microscopy (SEM) analysis showed that RHA has irregularly shaped particles with a porous, cellular structure. Similarly, chemical analysis of SSA revealed it contains over 60% active calcium oxide with minor oxides, and SEM analysis showed it has irregular semi-spherical particles with porous surfaces. The replacement of cement with RHA led to improved mechanical and durability properties in concrete, although workability was reduced. RHA also demonstrated resistance to chloride penetration. Combining RHA and SSA has the potential to produce stronger, more durable concrete, and could replace cement in high volumes in concrete production.