Inclusion of alkali-activated municipal slag cement–fly ash as a cement substitute can have an important outcome on the fresh mixtures and early-age strength of geopolymer mortar cured in different conditions. This study evaluates the effects of various quantities of activator on the workability and early-age strength of alkali-activated municipal slag–fly ash–based geopolymer mortar. Early-age compressive strength is measured under different curing conditions: steam curing, water curing, and air curing. In addition, early-age splitting tensile strength, flexural strength, and microstructure analysis using scanning electron microscopy (SEM) are examined for steam-cured mortar. Test results show that both curing regime and activator content in the main binder are significant factors influencing the performance evaluation of fresh mixtures and early-age strength of geopolymer mortar. A standard design equation is used to predict the compressive strength, and predications of splitting tensile and flexural strength of geopolymer mortar are calculated using another standard.

This study investigates the effect of varying ratios of fly ash as a partial replacement for fine aggregate on the performance of alkali-activated municipal slag composites. The strength and other properties of alkali-activated cementitious material (AACM) composites can be optimized by selecting the appropriate mix proportion. In this study, we used fly ash as a substitute for fine aggregate (FA/S) at varying ratios of 0.0, 5.0, 10.0, 15.0, 20.0, 25.0, and 30.0%, mixed with 50% water (W/SL), and 20% alkali activator (AL/SL) content instead of municipal slag (SL) as a core binder, cured in steam conditions. The effects of these substitutions on the initial mixing temperature, slump flow, compressive and splitting tensile strengths, and microstructure analysis of composites cured in steam conditions were investigated at 1, 7, 28, and 91 days. The evaluation of the experimental results revealed that increasing the ratio of fly ash substitution to fine aggregate by up to 20.0% led to a higher strength attributable to the composites, whereas when the extra substitution ratio of FA/S ranged from 25.0–30.0%, significant decreases in strength were observed. The composites’ strengths were estimated using the ACI 209 and ACI 318 design equations and compared to the measured strengths.

This paper presents the simultaneous effect of alkali activator and water/slag cement ratios on composites properties by full replacement of Portland cement at different ages under steam curing condition. Twelve mortar composites divided into four different groups were prepared using municipal slag cement and alkali activator of sodium meta-silicate by varying the ratios of alkali activator/slag cement and water/slag cement. The results revealed that the addition of municipal slag cement by full replacement of Portland cement was largely worthwhile for slag mortar composites under steam curing condition. The preparation of the mortars by taking various ratios of alkali activator/slag cement and water/slag cement contributed significantly in improving the compressive strength with an acceptable drying shrinkage to slag composites. Scanning electron microscopic technique was used to analyze the microstructure of slag composites at different ages. The ACI 209 and EC 2 design equations were used to predict the compressive strength.

This study explores the early-age performance of eco-efficient alkali-activated slag–fly ash (AASF) mixtures using high-calcium fly ash (HCFA) and low-calcium fly ash (LCFA) at varying alkali activator-to-slag cement (AL/SC) ratios (15%, 20%, and 25%) under steam, water, and ambient curing conditions. Mix designs were developed with a fixed water-to-slag cement ratio of 50%, while fly ash partially replaced fine aggregate at a 20% substitution level. Fresh and hardened properties were investigated. The results revealed that increasing the AL/SC ratio led to reduced workability and increased flow loss, especially in HCFA mixtures, due to their higher calcium content and finer particle size, which promoted early stiffening. In contrast, LCFA mixtures exhibited greater slump flow and better workability retention owing to their slower dissolution rate. Regarding compressive strength, steam curing produced the highest performance. At 25% AL/SC, HCFA mixtures achieved 70 MPa at 28 days, while LCFA mixtures reached 68 MPa. Water curing showed moderate strength development, whereas ambient curing resulted in slower gains. These findings emphasize the influence of fly ash type, AL/SC ratio, and various curing conditions in enhancing the performance of eco-efficient AASF mixtures.

The presence of fling step and forward directivity, as distinctive features of near-fault ground motions, can lead to substantial alterations in the seismic performance of reinforced concrete bridges. This study examines the seismic performance of reinforced concrete bridges with various deck slabs subjected to two distinct sets of earthquake events. One set is of forward-directivity records, and the other set is of fling-step records. Three-dimensional finite element models for the analyzed reinforced concrete bridges are constructed using the CSI-BRIDGE v26 software package, incorporating appropriate material and geometric nonlinearities. The developed bridge models are of three spans and have different deck slab systems, namely, box girder, RC girder, and hollow core slab bridges. Extensive nonlinear response time-history analyses of various configurations representing the examined RC bridges are performed to elucidate the impact of seismic loads, including forward-directivity and fling-step records, on the seismic response of supporting columns and deck slabs in the longitudinal direction. The numerical simulations indicate that ground vibrations with fling step significantly amplify the seismic response demands in both substructure and superstructure elements. Moreover, bridge type substantially influences the induced seismic responses, particularly supporting columns and deck slabs.

Since tires from end-of-life vehicles are not entirely biodegradable and pose a serious environmental problem, their disposal has become a significant global environmental concern. One technique to decrease these environmental issues is incorporating waste rubber to make sustainable green concrete. This study examined the usage of waste supplementary cementitious materials (SCMs) such as fly ash (FA), metakaolin (MK), marble powder (MP), slag (SL), and silica fume (SF) for surface precoating of crumb rubber (CR) to improve the mechanical properties of the produced crumb rubber concrete (CRC) by strengthening the bond between CR and cement paste in the interfacial transition zone (ITZ). The CR replaced (0, 15%, and 25%) of sand by weight in the preparation of CRC mixtures. A total of eleven CRC mixes were cast to investigate the fresh properties, compressive strength, and splitting tensile strength. In addition, the compressive stress-strain curve was investigated, and peak stress, peak strain, energy absorption, toughness, and modulus of elasticity have been evaluated. The outcomes showed that precoating CR using FA, followed by MK, has the strongest effect on increasing CRC compressive performance. The 25% substitution of sand with FA-treated CR increased compressive strength after 28 days, splitting tensile strength, peak stress, toughness, and modulus of elasticity by 34.7%, 23.7%, 34.8%, 26.1%, and 25.2%, respectively, in comparison to the same percentage of untreated CR. The proposed approach demonstrates a viable pathway for integrating waste materials and SCM-based technologies to develop high-performance, sustainable cementitious composites.