28-day Compressive Strength Research Articles

Performance of Molasses Waste as a Cement Replacement to Study Concrete Compressive Strength

To reduce the negative environmental impact of cement production and preserve natural resources, an experimental investigation was conducted to study the performance of concrete specimens at different curing ages and to determine the compressive strength of these specimens by replacing cement with molasses. Experimentation was carried out on the concrete specimens at a temperature range of 25 °C to 30 °C; six specimens were cast for each replacement ratio, except for 0.75% wt. of cement (86.55 g) and 1% wt. of cement (113.6 g), where five samples were considered for each ratio. The average 28-day compressive strength of the conventional concrete specimens came out to be 29 MPa, but increased to 40 MPa with the addition of 0.25% wt. of cement molasses (28.85 g). It was observed that as the percentage of molasses waste in the concrete mix was further increased by replacing the cement, the compressive strength of the concrete specimens increased gradually and then significantly decreased. The findings shed light on the prospect of using molasses waste instead of cement in the concrete mix. Also, it is worth mentioning that about 30% of the cost–benefit was obtained with reference to that of conventional admixtures available in the market for the production of concrete. However, it is notable that a long-term durability study needs to be conducted before making it viable. This work not only addresses a sustainable and innovative method of waste management (SDG12), but also contributes to low carbon emissions (SDG13). The novelty of this work lies in the fact that no such kind of study has been conducted in Pakistan so far, in addition to the very limited international literature available, and, in particular, no evidence on the compressive strength results at higher molasses dosages, i.e., 1% wt. of cement (113.6 g) and 2% wt. of cement (230.8 g).

Honeycombed pomegranate-like sludge ceramsite particles: Preparation with fly ash floating beads as the pore-forming template and performance optimization

Ceramsite used in construction and building are typically limited by high water absorption rates, the contradiction between lightweight and high strength, and severe performance fluctuations. This can be attributed to the fact that ceramsites are currently prepared by high-temperature sintering expansion, wherein viscosity and surface tension of the liquid phases shall perfectly match with the gas generation rate. On the other hand, sand washing sludge and fly ash are common solid wastes in construction and building and their environmentally friendly disposal are of great significance. In this study, honeycombed pomegranate-like sludge ceramsites with low density (packing density = 733.2–968.3 kg/m3), high strength (cylinder compressive strength = 11.2–18.8 MPa), and low water absorption rate (one-hour water absorption rate = 1.2–2.8 %) were prepared with sand washing sludge and fly ash floating beads as the raw material and the pore-forming template, respectively. Also, the effects of particle size and content of fly ash floating beads on the structure and performance of the as-prepared ceramsite were investigated. The results indicated that the pore structure of the as-prepared ceramsite was directly dependent on size and content of the fly ash floating beads, suggesting that the performance of the as-prepared ceramsite can be customized by tuning size and content of the beads. Additionally, lightweight aggregate concrete prepared by using the as-prepared ceramsites exhibited improved 7-day and 28-day compressive strengths and reduced thermal conductivity compared with concrete prepared by using commercially available ceramsites. Overall, this study presents the preparation of ceramsite particles with both high strength and low density by using fly ash and sand washing sludge, both of which are abundant solid wastes in constructions, thus contributing to solid waste recycling in construction.

Utilization of waste phosphogypsum in high-strength geopolymer concrete: Performance optimization and mechanistic exploration

Phosphogypsum (PG) is an industrial waste produced during the manufacture of phosphoric acid. In this study, dihydrate phosphogypsum (DPG), ground granulated blast furnace slag (GGBFS), fly ash (FA), Portland cement clinker (PCC), sulfate alumina cement clinker (SACC), water reducer, sand, and stone were combined to create a phosphogypsum-based geopolymer (PBG) concrete. Concrete mix design was carried out based on the principle of maximum packing density, and the effects of water reducer type, sand ratio, water-to-binder ratio, and DPG content on PBG concrete properties were investigated. Results indicated that compared to SiKa ViscoCrete 540P (SVC 540P) water reducer, Melflux PLUS 1087L (MP1087L) significantly enhanced the performance of PBG concrete. With a water-to-binder ratio of 0.34, a sand ratio of 32.2 %, and a PG:GGBFS:FA ratio of 5:4:1, the 28-day unconfined compressive strength (UCS) of the concrete exceeded 60 MPa. The concrete primarily consisted of phases such as dihydrate gypsum (CaSO4·2H2O), ettringite (Ca6(Al(OH)6)2(SO4)3(H2O)26), polymer (-Si-O-Al-), quartz (SiO2), albite (Na(AlSi3O8)) and Muscovite ((K,Na)Al2(Si,Al)4O10(OH)2). Using two mild alkalis as activators, PBG concrete can avoid the efflorescence often associated with geopolymer preparation and can cure at 20 °C. PBG concrete offers high strength, ease of preparation, and environmental benefits, providing a new avenue for the reuse of PG.

Influence of Grinding Aids on the Grinding Performance and Rheological Properties of Cementitious Systems

The cement industry is of great importance in terms of raw materials consumed, energy consumed, and greenhouse gases emitted. Grinding aids (GA) are used to reduce energy consumption and costs, as well as to reduce the amount of CO2 released into the environment. In this study, the effect of GA-polycarboxylate ether-based water-reducing admixture (PCE) compatibility on some fresh, rheological and hardened state properties of cementitious systems was investigated. In order to investigate the rheological properties and thixotropic behavior of the mixtures, a total of 51 cement paste mixtures were prepared, containing 4 different types (molasses, MEG, DEA and ethanol) and ratios (0.025, 0.05, 0.75 and 0.1) of GAs and 2 different ratios (0.08% and 0.16%) of PCE in addition to the control mixture. In addition, the effect of the used GAs on the grinding efficiency and compressive strength value was investigated. Additionally, the predictability of the type of GA, dosage and cure time using the Taguchi method was investigated. It was determined that the highest grinding performance was obtained in mixtures containing MEG. It was determined that in cement paste mixtures containing GAs, the dynamic yield stress and viscosity values generally decrease with the increase in PCE usage rate up to a certain value, and these values may increase if the PCE usage increases further. It was determined that such behavior is not present in cement paste mixtures containing GAs and that the structural build-up value of the mixtures generally increases with the increase in the PCE admixture usage rate. It was determined that the use of GAs had a positive effect on 28-day compressive strength.

Evaluation of Material Characteristics and Durability of Mixture of Carbon-Eating Concrete and Electric Arc Furnace Slag via Optimal Carbon Dioxide Curing

This study evaluates the material characteristics and durability of a mixture of carbon-eating concrete (CEC) and electric arc furnace slag. Due to the high C<sub>3</sub>A content present in the electric arc furnace reducing slag binder used in the CEC mix, the initial and final setting times of CEC are observed to be 18.8% and 7.0% faster than those of ordinary Portland cement (OPC), respectively. The optimal carbon dioxide curing condition is determined by varying the pressure and temperature variables within the scope of this study. The 3-day compressive strength of CEC under optimal carbon dioxide curing conditions is observed to exceed the 28-day compressive strength of OPC. The formation of calcium carbonate, which contributes to early strength, is confirmed via scanning electron microscopy and thermogravimetric analysis. Additionally, CEC exhibits significantly higher improvements in abrasion resistivity and chloride-ion penetration resistivity when subjected to carbon dioxide curing compared to OPC.

Mechanical properties and chemical microscopic characteristics of all-solid-waste composite cementitious materials prepared from phosphogypsum and granulated blast furnace slag

Industrial wastes, such as phosphogypsum, are characterized by high production and accumulation volumes, and significant pollution. A high-performance, all-solid waste, phosphogypsum-based composite cementitious material (PCCM) was developed by using a hybrid ball milling method and thermal activation to stimulate various industrial wastes. Optimization of rationing was analyzed using extreme variance, standard variance, and multiple regression models. The macro-engineering parameters of PCCM were evaluated through flexural and compressive tests. The mineralogical composition, functional groups, micro-morphology, and molecular structure of PCCM were examined through micro-testing. When the mass ratio of Ball milled calcined phosphogypsum (BCPG) to granulated blast furnace slag (GGBS) is 1.2:1, with a 4 % addition of calcium oxide and a water-cement ratio of 0.4, the 28-day flexural and compressive strengths, as well as the softening coefficients, of PCCM can reach 7.27 MPa, 40.1 MPa, and 0.922, respectively, closely matching the performance of C42.5 cement. Under the synergistic effects of the hydration reaction and an alkaline environment, the CaSO4 in the PCCM system hydrated and crystallized to produce gypsum-phase crystals, enhancing early strength properties by 60–174 %. As hydration continued, SO42- reacted with silicon and aluminum oxides, prompting secondary hydration of GGBS, and increasing AFt and C-(A)-S-H in the system. This research offers a new approach for the co-disposal and resource utilization of various solid wastes while identifying a cementitious material that can replace traditional cement in practical engineering applications.

Characteristics of alkali-activated composites containing blast-furnace slag aggregate and ferronickel slag powder

The use of alkali-activated composites and alternative aggregates reduces the carbon dioxide emissions of the construction industry and mitigates the problem of aggregate depletion. However, published investigations into non-cement composites containing ferronickel slag powder (FSP) and blast-furnace slag fine aggregate (BSA) are limited. The aim of this study was thus to assess the mechanical properties and durability of non-cement composites containing FSP and BSA. The mix with 10% FSP and 25% BSA was found to have the highest 28-day compressive strength, of approximately 42.2 MPa. For the mixes with 5% FSP, the 28-day compressive strength increased with an increase in BSA content. Charge-passed tests revealed that, after 7 days, the sample with 5% FSP and 50% BSA exhibited a total charge of approximately 907 C, classifying it as ‘very low’ according to ASTM C1202. By 56 days, the total charge for this sample reached a value of approximately 120 C, close to ‘negligible’ as per ASTM C1202. It was thus concluded that an appropriate BSA content effectively enhances the mechanical properties and durability of non-cement composites.

Sustainable utilization of phosphorus-rich sludge in cement composites: Multiscale evaluation and mechanistic analysis

The treatment of sludge poses challenges for resource utilization and environmental protection, and utilizing sludge as supplementary cementitious materials (SCMs) presents a viable solution. However, the phosphorus content significantly influences the cement hydration process. This study primarily investigates the feasibility of phosphorus-rich sludge (PRS) as SCMs and examines the effects of combining PRS with calcined clay on cement hydration. The research focuses on hydration heat, mechanical properties, microstructure, and durability of composites comprised of PRS, limestone, calcined clay, and ordinary Portland cement. The results indicate that PRS delays early hydration reactions, leading to a decrease in early compressive strength; after 7 days, the compressive strength is approximately 14.3 MPa (sample S20C10L15). However, over time, the strength increases to 34.1 MPa at 28 days, reflecting a 138.5 % increase compared to the 7-day compressive strength (with sample OPC exhibiting only 69.1 %). This correlates with the hydration exothermic peak occurring in the later stages and the transition of phosphorus's effect on cement hydration from inhibitory to non-inhibitory. The phosphorus in PRS partially replaces silicon atoms in C-(A)-S-H gel, forming C-S(A,P)-H gel. This process refines pore sizes within PRS cementitious materials, enhancing compressive strength over time. Early hydration inhibition and the subsequent pozzolanic reaction of PRS reduce portlandite content, which lowers carbonation durability and thermal expansion coefficient. However, the quaternary blend of PRS, limestone, calcined clay, and ordinary Portland cement demonstrates excellent mechanical properties. This study provides experimental evidence for reducing the environmental impact of PRS and exploring carbon reduction strategies in the cement industry.

Relationship between MO/(SiO2+Al2O3) of materials—amorphous gel structure—properties of the one-part FA-Slag-based AAMs

The study investigates the impact of different amorphous gel structure by MO (CaO+Na2O)/(SiO2+Al2O3) ratios (specifically 0.66, 0.69, 0.73, 0.76, 0.84, and 0.90) on the fresh and hardened properties of one-part alkali-activated materials (OP-AAMs) derived from fly ash-slag. Unlike traditional two-part AAMs, the "just-add-water" preparation process of OP-AAMs facilitates the transition of geopolymer products from laboratories to the engineering field. Higher (CaO+Na2O)/(SiO2+Al2O3) ratios in fresh pastes promote the dissolution of active aluminosilicate in the alkali-activators, resulting in the formation of Si-rich gel with low-Al amorphous gel. This leads to reduced setting time, increased fluidity, and the occurrence of a viscoelastic phenomenon in the fresh properties. Throughout the geopolymerization process, the main product with the shortest mean chain length and higher Si/Al ratios is the C-(N)-A-S-H and N-A-S-H gel in the (CaO+Na2O)/(SiO2+Al2O3)=0.76 composition, which exhibits the highest 28-day compressive strength of 46 MPa. The findings highlight the potential of OP-AAMs and provide insights into the adjustment mechanism of MO/(SiO2+Al2O3) ratios to optimize the properties of OP-AAMs for engineering applications.

Design of a novel ternary blended Self-Compacting Ultra-high-performance Geopolymer Concrete

In this research study, the Taguchi orthogonal array (TOA) optimisation method was used to design the optimum mixture proportions of ternary blended Self-Compacting Ultra-High-Performance Geopolymer Concrete (SCUHPGC). The SCUHPGC mixtures, cured at ambient conditions, included Ground Granulated Blast Furnace Slag (GGBFS), Fly Ash (FA), and Silica Fume (SF) as aluminosilicate sources and sodium hydroxide solution and sodium silicate solution as alkaline activators. The effects of six factors at three levels on the compressive strength of SCUHPGC were investigated. The considered factors were the binder content, the ratio of fly ash to ground granulated blast furnace slag (FA/GGBFS), the ratio of silica fume to binder content (SF/Binder content), the ratio of alkaline activator to binder content (AAL/Binder content), the ratio of sodium silicate to sodium hydroxide (SS/SH), and the concentration of sodium hydroxide solution. Twenty-seven SCUHPGC mixtures were evaluated. The slump flow diameter of the optimum SCHUPGC was 740 mm, which satisfies the requirements of self-compacting concrete. The maximum 28-day compressive strength of 132.7 MPa was achieved by the optimum SCUHPGC mixture, which contained a binder content of 1050 kg/m3, a FA/GGBFS ratio of 0.3, an SF/Binder content ratio of 0.05, an AAL/Binder content ratio of 0.4, a SS/SH ratio of 4.0, and an SH concentration of 12 M. The 28-day flexural strength and tensile strength of the optimum SCUHPGC mixture were 9.6 MPa and 4.9 MPa, respectively.

Utilization of incense stick ash as a supplementary cementitious material: Effects on strength, cement chemistry, and sustainability

Incense stick ash (ISA), a by-product generated from the combustion of biomass during religious rituals, presents challenges regarding its high-volume disposal despite some emerging technologies offering avenues for its reuse. This study aims to investigate the feasibility of utilizing ISA as a supplementary cementitious material and its impact on fresh and hardened properties, hydration kinetics, microstructure, and environmental and economic aspects of Portland cement (PC) pastes. Results reveal that incorporating 5–20 % ISA increases the cumulative heat release per gram of PC. Specifically, replacing 5 % of PC with ISA enhances the 28-day compressive strength, with an increase of 19.78 % compared to plain cement paste. However, further elevation in ISA substitution leads to a decline in compressive strength. The utilization of 5 % ISA refines the pore structure of samples and elevates the content of calcium silicate hydrate (C-S-H), particularly the proportion of high-density C-S-H. Additionally, carbonates present in ISA react with AFm to form monocarbon calcium aluminate, which stabilizes AFt and enhances the microstructural compactness of cement paste. Compared to plain cement paste, the paste with 5 % ISA exhibits lower coefficients for the cost of pastes per cubic meter, CO2 emission of pastes per cubic meter, and non-renewable energy consumption, underscoring the effective utilization of ISA and its role in promoting sustainability. This study will facilitate the application of ISA in cement-based materials and provide technical guidance for subsequent research.

Performance Optimization of Alkaline Multi-Industrial Waste-Based Cementitious Materials for Soil Solidification.

This study presents the development of eco-friendly cementitious materials for soil stabilization, based on alkaline multi-industrial waste (AMIW), using steel slag (SS), blast furnace slag (BFS), carbide slag (CS), fly ash (FA) and flue gas desulfurization gypsum (FGDG) as the raw materials. The optimal AMIW-based cementitious material composition determined through orthogonal experiments was SS:CS:FGDG:BFS:FA = 15:10:15:44:16. Central composite design (CCD) in response surface methodology (RSM) was employed to optimize the curing process parameters. The maximum 7-day unconfined compressive strength (7d UCS) was achieved under the optimal conditions of 18.51% moisture content, 11.46% curing agent content and 26.48 min of mix-grinding time. The 7d UCS of the AMIW-stabilized soil showed a 24% improvement over ordinary Portland cement (OPC)-stabilized soil. Rietveld refinement results demonstrated that the main hydration products of the stabilized soil were C-S-H and ettringite. After curing for 7 days to 28 days, the C-S-H content increased from 3.31% to 5.76%, while the ettringite content increased from 1.41% to 3.54%. Mercury intrusion porosimetry (MIP) and scanning electron microscopy (SEM) analysis revealed that with the extension of curing time, the pores of the stabilized soil become smaller and the structure becomes denser, resulting in an improvement in compressive strength.

Performance Study of Stabilized Recycled Aggregate Base Material with Two-Gray Components.

This article studies the practical road performance of recycled materials from construction waste, relying on the paving test section of the supporting project for the Qingdao Cross-Sea Bridge. The research focuses on the construction technology and road performance of using recycled construction waste materials in urban road sub-base construction. Through indoor tests such as sieving and unconfined compressive strength tests, relevant technical indicators were obtained and analyzed. Additionally, periodic core sampling, compaction tests, and rebound deflection tests were conducted on-site according to relevant standards to thoroughly investigate the specific effects of using construction waste in practice and to analyze and evaluate the actual feasibility of the materials for road use. The results indicate that the particle gradation of the construction mix in the test section aligns well with the target gradation, and the dosage of the mixing agent meets the design requirements. The 7-day unconfined compressive strength already satisfied the technical requirements for heavy and extremely heavy traffic on highways as specified in the "Technical Specifications for Construction of Highway Pavement Subbase" (JTG/T F20-2015), with the 14-day strength generally reaching 7 MPa. Core sampling revealed good aggregate gradation, smooth and straight profiles, and the thickness and strength of all parts meet the specifications. The compaction levels met the testing requirements, the surface deflection values showed a decreasing trend, and the deformation resistance was good, consistent with the general development patterns of semi-rigid sub-bases.

Mechanical, electrical, and piezoresistive properties of modified conductive recycled fine aggregate smart mortar

The application of recycled fine aggregates (RFA) in smart conductive mortar is of great significance for conserving natural resources and protecting the environment. However, the high water absorption and microstructural defects of RFA limit its widespread use in smart conductive mortar. This study employs an agar gel impregnation treatment containing graphite particles to improve the properties of RFA. The resulting modified conductive recycled fine aggregate (M-RFA) exhibited a 2.8 % reduction in water absorption. The workability, mechanical properties, electrical properties, and self-sensing capabilities of the modified recycled fine aggregate mortar (M-RFAM) were studied. It was found that the workability and mechanical properties of the smart conductive mortar prepared with M-RFA were slightly reduced but remained within acceptable ranges (28-day compressive strength greater than 33 MPa). At the same time, it achieved low resistivity and high strain-sensing sensitivity, with the highest strain-sensing sensitivity being 61.9 (30 times higher than ordinary strain gauges). The influence of loading rate and moisture content on the self-sensing ability of conductive mortar was also investigated, revealing a positive correlation between moisture content and stress-sensing ability. Furthermore, the study found that factors such as AC frequency, curing age, moisture content, and temperature significantly affect resistivity. These factors should be considered in practical applications and further research.

Data-driven inverse mix design for sustainable alkali-activated materials

Alkali-activated materials (AAMs) are promising alternatives to ordinary Portland cement (OPC), but standardized mix design approaches are limited. This study introduces a machine learning-based framework for inverse mix design of AAMs, predicting optimal mixes based on target properties and sustainability. The model considers eight key factors, including precursor reactivity, activator properties, and liquid-to-binder ratio. It operates in four steps: (i) constructing forward prediction models, (ii) generating new mix designs, (iii) evaluating workability and strength, and (iv) filtering for performance and sustainability. Experiments validated the model, targeting fluidity >100% and compressive strengths of 40 MPa (A40) and 50 MPa (A50). The A40 and A50 mixes achieved fluidities of 147.7% and 170.0%, and 28-day compressive strengths of 41.5 and 57.5 MPa. Both had lower environmental impacts (GWP, AP, and EP) compared to OPC-based mortars. This framework enhances AAM design efficiency and sustainability for broader applications.

Experimental Study on the Strength and Durability of Manufactured Sand HPC in the Dalian Bay Undersea Immersed Tube Tunnel and Its Engineering Application

The usage of manufactured sand concrete is widespread in modern engineering, and it is important to study its performance to improve the overall engineering quality. This paper presents an experimental study on the working performance and durability of 12 groups of manufactured sand high-performance concrete (MSHPC) with varying mix ratios, in the context of the construction of the Dalian Bay undersea immersed tube tunnel. The study reveals that the stone powder content significantly affects the physical and mechanical properties, as well as the durability, of manufactured sand concrete. At an approximately 9% stone powder content, the concrete achieves the highest slump and best workability. However, excessive stone powder reduces early crack resistance. Furthermore, an optimal stone powder content (ranging from 5% to 13%) enhances the compressive strength, with the 28-day compressive strength reaching 60 MPa at a 13% stone powder content, while the effect on the splitting tensile strength is negligible. The stone powder content does not significantly impact impermeability and frost resistance, but at 7–9%, the RCM method shows the lowest chloride ion diffusion coefficient. Additionally, a lower water–binder ratio enhances resistance to chloride ion diffusion. High-performance RCM concrete with a 9% stone powder content was used in the construction of the Dalian Bay Cross-Harbor Tunnel, achieving 28-day and 56-day compressive strengths of C45 and C50, respectively, an impermeability grade of P14, a chloride ion diffusion coefficient of 1.9 × 10−12 m2/s, and a frost durability index of 92%, meeting the project’s 100-year lifespan design requirements.

Strength, durability, and heat development characteristics of high-performance concrete containing ground coal bottom ash with low and high calcium

Currently, the availability of fly ash has reduced continuously due to the shutdowns of coal-fired power generating plant as climate change concerns have increased. Therefore, the aim of this paper is to find an alternative pozzolan by examining the employment of low- and high-calcium oxide (CaO) ground bottom ash which has been abandoned rather using in concrete production. The bottom ashes were blended with fly ash as a partial substitution of cement (OPC) by observing their generic effects on the compressive strength, cumulative heat generation, chloride ion penetration, and water sorptivity of high-performance concrete. The samples of bottom ash were prepared by oven drying, particle size cutting, and grinding to enhance the reactivity and consistency. High-performance concretes were made at a water-to-binder (W/B) ratio of 0.27 and partial replacement of OPC up to 50 % by weight of the binder. The results indicated that the concretes with 28-day compressive strengths of 101.0 and 109.0 MPa (21.6 % and 28.2 % stronger than OPC concrete) were produced with 50 wt% OPC replacement with high- and low-calcium ground coal bottom ashes (HCBA and LCBA), respectively. These findings suggest that HCBA and LCBA have high pozzolanic reactivity and high possibility for utilization as pozzolan or supplementary cementitious materials in concrete. In addition, the binary blended binders (OPC-HCBA and OPC-LCBA) and ternary blended binders (OPC-HCBA-FA and OPC-LCBA-FA) produced had better chloride ion penetration resistance, less cumulative heat evolution, and lower water sorptivity than 100 % OPC as a cementitious material. Partial OPC replacement by HCBA and LCBA improved the chloride ion penetrability class of OPC concrete from “very low” to “negligible.” The cumulative heat generation due to the pozzolanic reaction of HCBA and LCBA from the partial replacement of OPC up to 50 % reduced 30–44 % relative to the OPC-based mixture throughout during 72 hours after mixing. The CaO content strongly influenced early compressive strength development and cumulative heat evolution but had less impact on chloride ion penetration resistance and water sorptivity.

Chemical interference between graphene oxide and polycarboxylate superplasticizer, and the resulting impact on the concrete strength, workability, and microstructure

Graphene oxide (GO) nanoreinforcement is shown to significantly improve the strength and durability of concrete at the expense of mix workability. While polycarboxylate superplasticizers (PCSP) addition has improved GO-cement/mortar strength and workability in existing literature, this article examines if this improvement is translated to concrete with lower cement and water contents. PCSP and GO showed colloidal instability and particulate aggregation through surface charge measurements, presumably caused by divalent Ca 2 + ion interbridging between the GO and PCSP. This chemical interference results in a 26% reduction in 28-day compressive strength and a 20% decrease in the workability of PCSP-treated GO-concrete. Microstructural examination reveals significantly larger pores in PCSP+GO cement than in GO-cement or PCSP-only cement due to the chemical interference induced by PCSP-GO interactions in cement and concrete. Hence, PCSP and GO interactions must be further researched for practical use in concrete structures.

Synergistic impact of geopolymer binder and recycled coarse aggregates on the performance of concrete masonry units

This study examines the combined effect of geopolymeric binder and recycled coarse aggregates (RCA) on the properties of concrete masonry units (CMU). A target 1-day compressive strength of at least 13.8 MPa was attained for all mixes to satisfy the load-bearing strength requirements. Geopolymer mixes made with RCA at replacement rates of up to 100 % were evaluated and compared to a cementitious control mix made with natural coarse aggregates. The environmental and economic impacts were then integrated with the quantity of waste valorized and compressive strength in a multifunctional performance index. Experimental results showed that the utilization of geopolymers as a substitute for Portland cement in the production of CMU did not impact the oven-dry density but reduced the water absorption capacity by up to 26 %. Although the incorporation of RCA negatively impacted these two properties, their values remained within the acceptable range stated by the standards. The geopolymer CMU mix made without RCA had 9 and 25 % lower 28-day compressive and splitting tensile strengths compared to the cement control mix, respectively. Subsequent RCA replacement further reduced these mechanical properties. While the linear drying shrinkage was reduced upon substituting the cementitious binder with the geopolymeric counterpart, RCA replacement of up to 100 % increased the linear drying shrinkage to reach 0.091 %, exceeding the limit set by the standard. Overall, the CMU mix made with geopolymer binder and 75–100 % RCA was found to be optimal for load-bearing applications.

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.