Replacement Of Ordinary Portland Cement Research Articles

The basic characteristics of paste backfill materials based on highly active mineral admixtures: Part I. Preliminary study on flow, mechanics, hydration and microscopic properties

The cost performance of backfill materials in coal mines has long limited the widespread use of backfill technology. Therefore, developing backfill materials that are both cost-effective and high-performing is a pressing scientific issue that requires immediate attention. This study proposes replacing ordinary Portland cement (OPC) with highly active mineral admixtures, such as mineral powder and limestone powder, to prepare a green, low-cost, and high-performance coal mine backfill material. The use of mineral admixtures can improve the performance of the backfill material while reducing its environmental impact. The proposed approach is cost-effective and environmentally friendly. The study employed experimental tests and microscopic characterization methods, such as the slump test, hydration heat test, uniaxial compressive strength test, and microstructure test, to clarify the synergistic reaction mechanism of highly active mineral admixture-based paste backfill material (HAM-PBM). This clarification is helpful in regulating the macroscopic properties of hardened paste. The results show that: (1) The rheological properties of fresh HAM-PBM slurry are consistent with the Herschel-Bulkley model, and its fluidity meets the technical requirements for coal mine backfilling. The slump of fresh HAM-PBM slurry ranges from 140 to 145 mm, and the yield stress ranges from 3.188 to 12.819 Pa. (2) Highly active mineral admixtures significantly affect the early hydration process of HAM-PBM. The parameters of the hydration characteristics during the initial dissolution stage, acceleration stage, deceleration stage, and stabilization stage gradually decrease, while the duration of the induction stage gradually increases. This confirms that the early hydration activity of mineral powder (MP) and limestone powder (LF) is lower than that of OPC. (3) The uniaxial compressive strength (UCS) of the MP series exhibits an "anti-hook" change pattern, while the UCS of the LF series shows a decreasing change pattern. The microstructure, including the number of hydration products, microscopic density, and other characteristics, follows the same change pattern as the UCS. (4) Based on the synergistic reaction mechanism of hardened slurry, it is recommended that MP replace a maximum of 10 % of OPC and LF replace a maximum of 5 % of OPC. The need for composite replacement of OPC with MP and LF is clarified, resulting in a cost-effective coal mine backfill material. This study has contributed to the national "double carbon" policy and the low-cost backfilling application of coal mines.

Investigation of strength and water permeability of sustainable high-performance concrete containing high-volume ground bottom ash blended with fly ash and nano-silica

This investigation focussed on minimizing the Portland cement usage in developing sustainable high-performance concrete (HPC) as low-carbon concrete. High-volume ground bottom ash (GBA) was utilized as cement substitution in combination with fly ash (FA) and nano-silica (NS) for producing HPC with compressive strength of 100 MPa, and various concrete mixes were examined to assess its workability, mechanical performance, water permeability, and carbon emissions. The microstructure of the materials and pastes were also analyzed with X-ray Diffraction (XRD), Thermogravimetric Analysis (TGA), and Mercury Intrusion Porosimetry (MIP). GBA was used to replace Ordinary Portland Cement (OPC) at very high levels of cement replacement, ranging from 60 to 80 % by weight of binder. As ternary binders, 10 % fly ash and 2 % nano-silica (NS) by weight of binder were also used to replace GBA. The early-age compressive strength of HPC containing high-volume GBA increased by using 2 % of NS. Incorporating 10 % of FA into HPC reduced the superplasticizer requirement, enhanced workability, and exhibited slightly lower early strength. The compressive strength of HPC containing 58 % GBA, 10 % FA, and 2 % NS could be developed at 90 days was more than 110 MPa. Moreover, the investigation indicated that employing GBA in the mix represents environmental sustainability for the development of high-performance concrete.

Influence of Rice Straw Ash on Workability and Strength of Concrete

Cement manufacturing is a major contributor to the waste of energy as about 3.4GJ of thermal energy is needed to produce 1 tonne of Portland cement, not to mention the emissions of greenhouse gases like carbon di oxide due to the calcination of limestone during Portland cement production. These emissions have caused a dramatic rise in global warming. There is a pressing need for innovative recycling technology that can reduce the negative effects of waste on ecosystems and people. Rice straws are the waste produced after the threshing of rice. The goal of this study is to investigate the influence of rice straw ash on workability and strength of concrete. The rice straw used was the straw of a specific rice variety locally called mass I gotten from Akpugo, Enugu, Nigeria. The rice straw was calcined by open burning to produce the rice straw ash (RSA). The materials used were preliminary tested to determine their physical properties and chemical composition. The rice straw ash was used to replace Ordinary Portland Cement (OPC) at 0, 5, 10, 15, 20 and 30% respectively. The workability and compressive strength test were done for all replacement levels. Using slump test, the concrete workability was evaluated. For this study, 72 cubes were cast, cured in water for 7, 14, 21, and 28days before been tested under compression. From the investigation, percentage increase in RSA replacement decreased the concrete workability. The sample containing 0%, 5%, and 10% RSA attained 9%, 6.1% and 2.2% more strength compared to the design strength at 28th day of curing. While the 15%, 20% and 30% attained 17.3%, 28.9% and 67.6% lower strength compared to the design strength at 28th day of curing. The experimental result was analysed using statistical product and service solution (SPSS) and excel spreadsheet regression (ESR). This study suggests that the optimum replacement level of rice straw ash from structural reinforced grade 25 concrete point of view is 10%. The predictive models were tested and found to be adequate.

Microscopic analyses and performance characteristics of granite powder blended cement

This research investigates the characteristics of Granite Powder (GrP) and its potential use as a partial replacement for cement in mortar production. The GrP samples were analyzed via microscopic techniques. The effects of GrP Blended Cement (GrPBC) were examined on the workability and mechanical characteristics by partially replacing Ordinary Portland Cement (OPC) with 0–40 wt% GrP in 4 wt% increments. Life cycled assessment in terms of Embodied Energy (EE) and Global Warming Potential (GWP) of GrPBC-based mortar were assessed based on cradle-to-gate boundaries and the sustainability and economic indexes were determined at 28 days compressive strength. The study proposed new models to predict the compressive strength of GrPBC with respect to Water to Binder (W/B) ratio. The presence of active minerals depicts GrP as pozzolanic materials. The optimum replacement level of GrP in the blended mix, based on the fresh and hardened properties of GrPBC, is 20 wt% to achieve 75% of the strength activity index. GWP and EE declined as the GrP in the mixtures rose. The best sustainable and economic prospects were attained at the 25 wt% GrP replacement level. The compressive strength and the W/B ratio are highly correlated. Thus, GrP has proven to be a sustainable construction material in the construction sector.

Suitability of rapid chloride migration tests for determining the migration coefficient in mortars made from different novel binder types

AbstractThe main cause of corrosion of reinforcing steel, especially in infrastructure structures, is the penetration of chlorides, which can lead to high corrosion rates at the reinforcement steel. A frequently used accelerated test method to evaluate the chloride penetration resistance of concrete and mortars is the rapid chloride migration (RCM) test. The test was initially developed for ordinary Portland cement (OPC) based materials and involves spraying an indicator solution onto split test specimens to determine the penetration depth of the chloride ions. The pore solution compositions of new types of binders differ from OPC‐based materials, which can affect the reaction of the indicator solution. To investigate the suitability of the RCM test, the chloride content in the depth of the color change was determined in mortars made from different types of novel binders. The results show that the test provides reliable results for the binder types with partial replacement of OPC by supplementary cementitious materials. For binder types without OPC, there is a deviation in the migration coefficient due to a differing chloride concentration that triggers the color change.

A comprehensive review of synthesis, characterization, and applications of aluminosilicate materials-based geopolymers

The increase in the cement industry's production, especially the production of Ordinary Portland Cement (OPC), increases the amount of CO2 released into the atmosphere, one of the main greenhouse gases responsible for global warming, with harmful effects on the environment and human health. Against this background, geopolymer concrete is a new type of inorganic polymer material that has attracted the attention of researchers in the building area, due to recycling waste by-products to replace OPC and reducing greenhouse gas (CO2) emissions during its manufacture. It also exhibits better mechanical, thermal, chemical, and electrical properties than OPC-based concrete. In the same environmental context, this material has also attracted the attention of researchers in the wastewater treatment area, because of its specific surface area and the capability of adsorption, photodegradation, and encapsulation of organic and inorganic pollutants. The principal focus of this paper is to provide an in-depth overview of the works that have been undertaken to explore geopolymer-type materials. The paper will attempt to develop a comprehensive database, based on the last research works published between 2010 and 2023 with about 247 references, which explains the elaboration, characterization, and application of these materials in several fields. Therefore, it is estimated that geopolymer composites are promising future candidates for recycling industrial solid waste, the partial or total replacement of OPCs in the construction industry, and the development of adsorbents and catalysts for wastewater treatment.

Strength Performance of Concrete Containing Rice Husk Ash as Cement Replacement in Presence of Polypropylene Fiber

This study focuses on the utilization of Rice Husk Ash (RHA) as partial replacement of Ordinary Portland Cement (OPC) in concrete in addition with Polypropylene (PP) fiber. The main goal of this study was to decrease dependence on OPC and address environmental waste generated through rice mills. This study considered concrete cubes prepared through 1:2:4 ration with 0.50 water-cement ratio with and without RHA and PP fibers. The water curing was done for 7 and 28 days, with three specimens for each proportion, and the average value was considered as the result. It was observed that the compressive strength of M2 concrete which containing 10% RHA was noticed 7% higher than the control mix concrete and declared as 10% RHA as optimum dosage. Next, the performance in terms of compressive strength of concrete containing optimum dosage of RHA in presence of PP fibers of three different lengths were also evaluated and found that the 0.1% of PP fiber of 0.5 inches length gives the 25% higher strength performance as compared to the control mix and 17% higher than the concrete containing 10% RHA only at the age of 28days. Hence, this study concluded that the replacing OPC cement with 10% RHA produces satisfactory strength performance and incorporation of PP fiber gives better strength performances.

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.

Optimization of Ca/Si ratio in schists to enhance the pozzolanic supplementary cementitious material for OPC blending

AbstractSupplementary cementitious materials (SCMs) are partial substitutes for ordinary Portland cement (OPC) to reduce cost, the production of carbon dioxide (CO2), and fossil fuel consumption. Recent studies illustrated the effectiveness of calcined kaolinite clay as a proper partial replacement for OPC. Hence, schist‐type materials containing sufficient clay contents are regarded as promising candidates for OPC replacement. This study focuses on the possible use of activated calcium carbonates (CaCO3) to augment pozzolanic reactions of schists as a substitute for OPC. The use of activated calcium carbonates proved to be successful in expediting pozzolanic reactions and facilitating the formation of additional calcium aluminosilicate hydrate (C‐A‐S‐H). In this study, the optimal strength performance for blended cement was achieved by adjusting the total carbonate content to 30 wt.% of the schist. The decision to introduce carbonate to the schist was guided by calculations determining the need for an excess of calcium ions to fully harness the potential for C‐A‐S‐H formation. Virgin and augmented schists were activated by up to 80% of their respective potentials by heat treatment. Phase content and decomposition behavior of the active components were investigated by thermogravimetric analysis (TGA), x‐ray diffraction (XRD), and scanning electron microscopy (SEM). Cement paste samples incorporating 30 wt.% replacement of OPC with activated schist SCMs were prepared. The phase distribution and compressive strengths of these samples were assessed at hydration intervals of 2, 7, 28, 50, and 90 days. Cement formulations with activated calcium‐augmented SCMs exhibited compressive strength values at 109%, 101%, 96%, 95%, and 94% compared to pure cement paste at 2, 7, 28, 50, and 90 days, respectively. These values surpassed 90% of the compressive strength of pure OPC at equivalent hydration time points.

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.

Influence of Ultrafine Steel Slag Powder Content Upon Cement Mortar

Steel slag (Electric Arc Furnace Steel Slag) is a by-product left over from the conversion of iron to steel in steel industries. This paper reports the results of an experimental study on partial replacement of ordinary Portland cement (OPC) with steel slags powder produced in Libya (Libyan Iron and Steel Company). The effects of various replacement ratios of ultrafine steel slag powder to Portland cement (i.e., 10%, 20%, 30%, 40%, and 50%) on the workability, mechanical, physical and chemical properties were studied. The fineness of steel slag powder was standardized by using a 63 μm sieve. The properties of cement pastes and mortars with ultrafine steel slag powder were tested including water requirement of normal consistency, setting time, soundness, fluidity, dry bulk density, total porosity, water absorption capacity. compressive and flexural strength. The results showed that for cement pastes with ultrafine steel slag powder, the normal consistency water requirement were increased significantly. Both the initial setting time and final setting time were also accelerated than that of the control sample. The partial replacement of cement by ultrafine steel slag powder decreases the compressive and flexural strength, but increases the fluidity which improves the workability of the mortar. The results showed that the optimum content of ultrafine steel slag powder as a replacement of OPC was 10%.

Early mechanical strength, hydration mechanism and leaching behavior of alkali-activated slag/fly ash paste filling materials

The enhancement of the early strength of the filling body is regarded as a critical technology for shortening the mining & filling cycle and achieving efficient production. It is a high-value utilization pathway to entirely replace Ordinary Portland Cement (OPC) with industrial waste residue. Hence, in this research, ground granulated blast furnace slag (GGBFS) and fly ash (FA) were selected as aluminosilicate precursors. The effects of single-component and binary activation of Na2SiO3, Na2SO4, Na2CO3, NaOH, NaAlO2 and triethanolamine (TEA) on the mechanical strength of backfill were systematically investigated. The microstructural evolution mechanism of hydration products was elucidated using XRD, TG-DTG, SEM and MIP analyses. The leaching characteristics and immobilization mechanism of heavy metals were further revealed. The experimental results indicated that the activator contributed an alkaline environment and active ions to the initial hydrolysis reaction of precursors and the polycondensation reaction of silica tetrahedra and aluminum tetrahedra with Ca2+ drove the hardening and development of the hydration products. Na2SiO3 exhibited the superior activation effect among single-component activators, while the binary activator presented notable “promoting and inhibiting characteristics”. Moreover, the binary activator composed of 4% Na2SiO3 and 4% NaAlO2 conducted the highest compressive strength at 3 d and 7 d. The dominant hydration products of the backfill were ettringite, C-S-H gels, C-A-S-H gels and zeolite-like products. The density of microstructures and the crystallinity of hydration products were significantly enhanced ascribed to the synergistic and complementary effects of Na2SiO3 and NaAlO2. Heavy metals were immobilized by the hydration products through physical encapsulation and chemical bonding, and the leaching concentrations of all heavy metals (Pb, Cd, Cr(Ⅵ), Zn, Mn, As and Cu, etc.) were lower than the standard limits of Class III in GB/T 14848-2017.

Service life modelling of carbonated reinforced concrete with supplementary cementitious materials considering early corrosion propagation

The importance of considering corrosion propagation in service life design of carbonated concrete with supplementary cementitious materials (SCMs) has been highlighted by the decline in carbonation resistance caused by partial replacement of ordinary Portland cement (OPC) with SCMs. This study proposes a novel Carbonation-induced Early Corrosion Propagation based Service-life Assessment Model (CECP-SAM) for carbonated SCM concrete, which is characterized by the considerations of semi-carbonation zone and macrocell corrosion in corrosion propagation with an incipient crack as end of service life. Experimental and field data were used to verify CECP-SAM. The effects of exposure conditions, SCM replacements, water/binder ratio, cover thickness, rebar diameter, semi-carbonation zone and macrocell corrosion on service life are presented. Results indicate that the partial replacement of OPC with pulverized fuel ash (PFA) and ground granulated blast furnace slag (GGBS) can significantly decrease service life from 66 years to 8 years and 17 years, respectively. Corrosion propagation can result in a 91% reduction in service life but service life can be extended from less than 20 years to more than 90 years by considering early corrosion propagation. Practical equations are proposed to facilitate performance-based service life design. Prescriptive limits are also provided for service lives of 50 and 100 years.

Fresh Properties, Strength, and Durability of Fiber-Reinforced Geopolymer and Conventional Concrete: A Review.

Reducing the environmental footprint of the construction industry in general and concrete in particular is essential. The addition of synthetic and natural fibers to concrete mixes at appropriate dosages enhances durability and strength and extends the lifespan of concrete infrastructures. This study reviews the geometric and mechanical properties of selected fibers such as steel, basalt, polypropylene, polyvinyl alcohol, polyethylene, glass, carbon, and natural fibers and their impact on concrete fresh, mechanical, and durability properties when combined in different configurations. The study focuses on the effect of blending fibers with concrete mixes that use alkali-activated binders based on recycled industrial byproducts such as slag and fly ash and thereby contribute to reduction of CO2 contribution through complete or partial replacement of Ordinary Portland cement (OPC). As a result, the effect of binder content, binder composition, alkaline activator concentration, and water-to-binder (w/b) ratio on fresh properties, mechanical strength, and durability of concrete with blended fibers is also evaluated in this study. The properties of fiber-reinforced concrete with alkali-activated binder and conventional OPC binders are compared. Fiber-reinforced concrete with alkali-activated binders that are based on industrial byproducts may represent sustainable alternatives to conventional concrete and offers competitive fresh and mechanical properties when fiber properties, fiber content, w/b ratio, binder type, and dosage are carefully considered in concrete mix design.

Full-scale static behaviour of prestressed geopolymer concrete sleepers reinforced with steel fibres

Profusive cracking leading to the deterioration of prestressed concrete sleepers has retained the sleepers from being exploited to their full extent. In addition, excess utilization of cement in producing the same has paved the way for developing its counterpart, geopolymer concrete (GPC), involving primary industrial residues as their precursors. This study presents a comprehensive investigation into the development and performance of high-strength geopolymer concrete sleepers for railway applications. The research focuses on the complete replacement of ordinary Portland cement with Fly ash and Ground Granulated Blast Furnace Slag in the geopolymer concrete mix, for mainline prestressed railway sleepers following Indian Railway Standards (IRS). Notably, the study includes experimental validations of long steel fibers as secondary reinforcement to the primary prestressing strands, aiming to enhance the ductility of the member. Experimental validations were performed on full-scale (1:1) sleeper members under static loading conditions. The main aim of this article was to assess the load carrying capacity at cracking and ultimate limits, rail seat bending moment, ductility indices, failure mechanism, electrical impedance, bond strength, and the eco-efficiency for the proposed prestressed geopolymer concrete sleeper members (with and without steel fibres) with reference to the conventional prestressed cement concrete sleepers. The considered GPC mix was found to achieve higher load and moment carrying capacity by about 8.3% and 8.54% respectively compared to the conventional concrete mix. The addition of steel fibres in the GPC increased the load and moment capacity of sleepers by 23% and 24.21% respectively. Additionally, the steel fibre reinforced GPC showed improved displacement ductility demand over the plain geopolymer concrete averaging 25%, 28.5%, and 3% corresponding to ultimate, failure, and residual ductility index respectively. Though inclusion of steel fibers improves the performance of sleepers in terms of load and ductility, they were found incompatible with regard to the electrical impedance property when used in conjunction with the pre-stressing strands.

Enhancing the environmental sustainability of water treatment sludge (WTS) disposal through blended binder solidification/stabilisation

Managing water treatment sludge (WTS) is challenging due to its continuous production and environmental impact. Traditional disposal in landfills is standard but risky for groundwater contamination. Researchers are exploring a more environmentally friendly method using a blend of binders, partially replacing Ordinary Portland Cement (OPC) with waste materials like Waste Paper Sludge Ash (WPSA), Palm Oil Fuel Ash (POFA) and Fly Ash (FA). These materials not only help reduce environmental waste but also decrease cement usage. The study assesses the Atterberg Limits of the treated sludge to design the appropriate solidification/stabilisation (S/S) method, providing essential data on its physical and mechanical properties Using waste materials as binders effectively stabilises the sludge, reducing reliance on cement, cutting disposal costs, and minimizing environmental pollution. The study identifies WPSA as the most suitable replacement, offering self-cementing properties, and demonstrates that combining WPSA OPC, and WTS creates a stable mix with liquefaction resistance. This approach presents a promising, cost-effective, and environmentally solution for WTS management.

Numerical Study of Potential Delayed Ettringite Formation in Cemented Nuclear Wasteforms

This paper presents a numerical study to investigate delayed ettringite formation (DEF) that may pose a long-term durability risk by altering the microstructure with consequent swelling leading to cracking. A chemo–thermal model is used to predict the evolution and distribution of temperature and hydration phases in a wide range of blended cements. In particular, the influence of nuclear waste loading, waste package size, and the addition of supplementary cementitious materials (SCMs) on DEF is systematically and numerically investigated. The analyses show that higher amounts of ordinary Portland cement (OPC) and waste loadings result in higher hydration temperatures and consequently increased DEF potential by enhancing sulfoaluminate dissolution and hydrogarnet precipitation. Partial replacement of OPC with SCMs reduced hydration heat and mitigated DEF risks. The analysis indicated that the DEF evolution may be different for waste packages of different sizes due to a shift from sulfate-controlling to aluminate-controlling reactions at high temperatures. Interestingly, higher temperatures did not necessarily induce higher DEF potential due to the excessive precipitation of aluminates in the form of hydrogarnet. This research enriches our understanding of DEF’s complex behavior, providing valuable insights for engineering applications beyond civil engineering, such as nuclear waste conditioning.

Assessment of the viability of pozzolanic activity of copper slag for use as supplementary cementitious material in ordinary Portland cement

The production of ferrous as well as non-ferrous metals generates slag as a byproduct material. Ferrous slags are extensively used in the construction sector as supplementary cementitious material (SCM) and aggregates. In this regard, the investigation of potential applications in similar areas for slags derived from the production of non-ferrous metals can help to address issues associated with their disposal, dumping, environmental concerns, etc. The primary aim of this research is to assess the pozzolanic activity of copper slag (CS), a type of non-ferrous slag. This investigation is conducted to replace a portion of ordinary Portland cement (OPC) incorporating CS as an SCM for sustainable construction. To assess the reactivity of the CS, comparisons were drawn with a known pozzolanic material fly ash (FA), and an inert material quartz powder (QP). The processing of raw CS (granular material) was carried out using a laboratory scale ball mill to achieve varying fineness to evaluate the effect of specific surface area (SSA) on reactivity. Initially, the investigations were conducted on paste samples of OPC-CS and suspensions of CS-calcium hydroxide (CH) and were later extended to mortar studies. Mechanical characteristics such as compressive strength and open porosity of mortar specimens were determined to correlate with the paste studies results. The findings suggest that CS does exhibit pozzolanic characteristics although its reactivity is comparatively lower than that of FA. An increase in the fineness of the CS resulted in enhanced pozzolanic activity. Analysis of the hydrated suspension samples showed the formation of Fe-siliceous hydrogarnet phase indicating “Fe” from CS was involved in the reaction with CH. Although OPC-CS mortar samples exhibited similar open porosity compared to OPC-QP mortar samples, the interfacial transition zone (ITZ) porosity in mortar samples of OPC-CS was observed to be reduced indicating the densification of the region due to the pozzolanic reaction of CS. The permissible replacement of OPC with CS as a substitute for FA can be adjusted according to the material's fineness and the desired compressive strength.

Effect of harsh environment on cement mortar containing natural pozzolans

This investigation aims to study the effect of the harsh environment on cement mortar containing pumice powder (natural pozzolana) as a partial substitute for ordinary Portland cement (OPC). The harsh environmental conditions applied in this study consisted of seawater supplemented with 5% of sodium sulfate (Na2SO4). Mortar mixtures were produced by replacing 0%, 5%, 10%, and 20% of the OPC mass with natural pozzolana (NP). Mortar samples were treated under two conditions. First, the mortar samples were immersed in tap water. Second, mortar samples are immersed in harsh environmental conditions. In the harsh environment, mortar samples were subjected to 90 cycles of dry-wet, 48-hour drying, and 48-hour wetting over a period of 360 days. Compressive strength, flexural strength, strength loss, change in length, water absorption, and initial surface absorption tests were performed on specimens aged 7, 28, 90, 180, and 360 days. Besides thermogravimetric and microstructure analysis of cement samples that were conducted at a test age of 180 days. The inclusion of NP as a partial replacement of OPC at a rate of 10% improved the results of compressive and flexural strength and achieved the lowest rates of porosity and water absorption of the mortar samples. The inclusion of NP as a partial replacement for OPC reduced the damage caused by the harsh environment.

Performance of recycled concrete aggregates based self-compacting concrete containing coal combustion ashes and silica fume

The objective of the current study is to evaluate the performance of Recycled Concrete Aggregates (RCA) based Self-compacting Concrete (RCA-SCC) comprising coal ashes and Silica Fume (SF). Coal ashes [Fly Ash (FA) and Coal Bottom Ash (CBA)] were incorporated as partial replacement for Ordinary Portland Cement (OPC) and Fine Natural Aggregates (FNA), respectively, while RCA were incorporated in place of Coarse Natural Aggregates (CNA). In order to compensate for the anticipated performance loss caused by the incorporation of RCA, a fixed percentage (10%) of SF was used as filler. The performance of aforesaid SCC was evaluated through various laboratory tests in fresh and hardened state. Five different substitution levels of CNA with RCA (0–100%), parallel with constant substitution level of FNA with CBA (10%) and OPC with SF + FA (10% + 20%) have been used throughout the investigation. Overall, the experimental outcomes along with regression results confirmed the potential of RCA-SCC prepared with CBA. RCA-SCC mix (25%) with coal ashes (FA + CBA) resulted in nearly equivalent performance to that of the reference SCC mix. Finally, the outcomes imply the successful contribution of SF, coal ashes (CBA + FA), and RCA leading towards the sustainable development of non-conventional SCC with identical performance.