International Concrete Abstracts Portal

This research focuses on developing a mixture design for highstrength geopolymer concrete (HSGPC) complying with the highstrength concrete criteria mentioned in Indian standards. This study focuses on optimizing the content of alkaline activators and binders proportionately. The compressive strength of different proportions of geopolymer mortar was carried out meticulously to determine the optimal proportions of solution-binder (S/B) and sodium silicatesodium hydroxide (SS/SH) ratios. The aforementioned ratios were optimized using the Technique for Order of Preference by Similarity to Ideal Solution (TOPSIS) analysis for further calculation. The mixture proportions for Grades M70, M80, M90, and M100 were determined and verified through experimental validation. To assess the suggested mixture design, a slump test was conducted to quantify the workability, subsequently followed by the evaluation of compressive strength after 24 hours, 7 days, and 28 days. After achieving the desired workability, promising compressive strength was observed as 76, 89, 93, and 104 MPa at 28 days. Finally, the mechanism of strength increment was investigated using various characterization techniques, such as X-ray diffraction (XRD) and scanning electron microscopy (SEM) equipped with energydispersive spectroscopy (EDS). The SEM/EDS analysis of the HSGPC proves the dense microstructures of different gel formations. The proposed mixture design procedure falls under the target strength-based method category. It has successfully yielded a strength of 104 MPa for ground-granulated blast-furnace slag (GGBS)-based geopolymer concrete incorporating coarse and fine aggregates.

The current paper investigates the effects of partial cement replacement with nano-titanium dioxide (nano-TiO2 [NT]) in varying weight proportions in concrete. In the C20/25 grade of concrete, NT was added by weight of cement with partial replacement of 0, 0.5, 1.5, 2.0, 2.5, and 3.0% using portland pozzolana cement. The physical and mechanical properties of the resulting concrete were assessed, as well as aspects of durability such as sorptivity and nondestructive tests (NDT) such as ultrasonic pulse velocity (UPV). Compared with the control mixture, the fresh concrete produced showed a drastic reduction in slump with increasing percentage of replacement, with a 54% reduction at a 3.0% replacement. Furthermore, for 1.5% NT, the compressive, flexural, and splitting tensile strengths peaked at 7, 28, 56, and 90 days, after which the values decreased. The addition of NT improved the homogeneity and integrity of the resulting concrete based on the UPV values. As the percentage of NT increased, chloride penetration decreased. From microstructural studies, it can be concluded that NT acts as a filler material and can be used as a partial replacement for cement in concrete up to 2% by weight.

The rapid workability loss of alkali-activated materials (AAMs) has been a major obstacle limiting their on-site application. In this study, two conventional high-range water-reducing admixtures (HRWRAs) (made of polynaphthalene sulfonate [PNS] and lignosulfonate [LS] salts), which have been reported to be effective in some specific AAM mixtures, were separately applied in alkali-activated slag (AAS) concretes. A comprehensive testing program was performed to study their effect on reaction kinetics, rheology evolution, and strength development. Results showed that sodium silicate-activated AAS mixtures exhibited lower yield stress than those activated by sodium hydroxide. In hydroxide media, PNS and LS remained effective in reducing yield stress and increasing slump value, while they both failed to improve the rheological behavior of AAS activated by silicate. Moreover, the inclusion of 2% admixtures did not result in much strength reduction in either activator, although LS showed a retardation effect and subsequent increase in the setting time in the fresh state.

In this experimental study, the workability and bleeding properties of cement-based grout mixtures combined with fly ash (FA) and colloidal nanopowder (n-Al2O3) were investigated, and some prediction models were developed with an artificial neural network (ANN). Marsh cone flow time, mini-slump spreading diameter, and Lombardi plate cohesion of the grout samples were measured based on the workability test. Test results showed that the use of FA as mineral additive in the grout samples positively contributed to an increase of the fluidity of the grout samples as expected. Considerable effects were observed on workability features of grout mixtures with the addition of nano alumina because of having a large specific surface area. In addition, the use of nano alumina together with FA in grout mixtures contributes to the stability of these mixtures by looking at changes in bleeding values. Using the experimental data obtained, an ANN model was developed to predict the values of Marsh cone flow time, mini-slump spreading diameter, and plate cohesion. The developed ANN model can predict mini-slump spreading diameter with an error rate of –0.04%, Marsh cone flow time value with an error rate of –0.23%, and plate cohesion value with an error rate of –1.07%.

The workability and mechanical performance of one-part alkali-activated self-consolidated mortar (AASCM) differ substantially from ordinary cementitious systems. However, it has scarcely been studied. This study examined the feasibility of producing “just add water” AASCM mixtures prepared by single, binary, and ternary precursor. Different tests, including the flowability and hydration heat, were evaluated to explore potential interactions between various ingredients. The hardened performance was evaluated based on achieved compressive strength at ages 7 and 28. Differential scanning calorimetry was used to evaluate various hydration products’ development over the investigated period. This study’s findings highlighted the high potential to produce green, easy-to-handle, one-part slag-based AASCM with fresh and hardened performance. Results showed that ternary mixtures exhibited higher flowability values than binary and single mixtures, except binary mixtures with fly ash. Furthermore, the modified particle size distribution of binary activated systems resulted in higher strength levels than single mixtures.