International Concrete Abstracts Portal

Due to the excellent deformation coordination ability and permeability, bentonite has been widely introduced to modify concrete in underground geotechnical engineering. However, the underlying mechanism for bentonite modification remains unexplored. A series of experiments was performed to clarify the modification mechanism of bentonite. The results showed that all strengths decreased upon bentonite addition, while high toughness was achieved. The micro-test results revealed that bentonite promotes the dissolution of calcium hydroxide (CH) and the nucleation of calcium silicate hydrate (C-S-H) in the interfacial transition zone (ITZ). The hydration products produced by the reactive ions and ultrafine bentonite particles continuously reduced the porosity and Ca/Si ratio in ITZ, strengthened the interface bonding, and controlled the coalescence of microcracks. Inversely, bentonite particles tend to adsorb large amounts of water and hinder the available water from accessing cement grains, which results in an increased porosity and slower hydration progress of cement grains. The loose microstructure cannot be compensated for by reinforced interfacial bonding and inevitably results in the deterioration of mechanical performance in composites.

In this work, novel polycarboxylate admixtures were synthesized by two different free radical polymerization systems of methacrylic acid (MAA) and methoxy polyethylene glycol methacrylate (MPEG-MA) for PC-1, and acrylic acid (AA) and iso amyl alcohol polyethylene glycol (IAA-PEG) for PC-2. Thioglycolic acid as a chain transfer agent and ammonium persulphate as an initiator were used. The synthesized carboxylic polymers were characterized using FTIR, H-NMR, gel permeation chromatography (GPC), and thermogravimetric analysis (TGA). The influence of the chemical structure of polycarboxylates on the rheology of the concrete, as well as the prognosis of the superplasticizer’s development, is also presented through measuring water consistency, setting times, flow table, slump test, Zeta potential, and compressive strength. The cementitious products were investigated with X-ray diffraction (XRD) and scanning electron microscope (SEM). The developed superplasticizers have shown good dispersion effects and slump performance in workability and fluidity retention tests, adsorption performance, and scanning electron microscopy performance. Intriguingly, the PC-1 and PC-2 mixes achieved flow table values of 230 and 200 mm, respectively. The compressive strength values at various curing ages up to 28 days exhibited double and triple values compared with the control sample. Additionally, compared to the control ordinary Portland cement paste, a reduction of water-to-cement ratio of about 0.25 and the development of excessive hydration products give PC-1 and PC-2 extensive pastes a more dense and compact structure in XRD and SEM investigation.

The growing generation of construction and demolition waste necessitates the development of effective recycling strategies to address environmental concerns. This study investigated the replacement of natural fine aggregate (NFA) with recycled fine aggregate (RFA) at 0, 50, and 100% using two treatment methods: (i) sodium silicate (SS)–silica fume (SF) pre-soaking treatment (SS-T) and (ii) organic treatment (OA-T) with bio-additives derived from Persea macranta, Haritaki, and Ciccus glauca roxb. A quantitative comparison of the aggregate and mortar quality was conducted for each method. The combined application of SST and OT demonstrated an 85% improvement in workability and a 68% reduction in water absorption for RFA. Mortar experiments revealed up to 76% improvement in compressive and flexural strengths compared with untreated RFA mortar. Microstructural analyses (SEM, EDS, XRD, and FT-IR) confirmed the enhanced bond strength and mineral composition. This study highlights the potential of SST and OT to produce durable, high-performance RFA mortars using locally available, economical bio-additives.

ASTM C31/C31M describes the procedure of making concrete specimens in the field. Its origin can be traced to 1920, proposing rodding or stroking each 100 mm thick layer 25 to 30 times. Concrete technology has evolved tremendously over the last century, but specimens are still prepared following this 100-year-old methodology. This paper investigates the density and compressive strength of concrete cylinders for different consolidation procedures. Mixture design variations include paste volume, water-cement ratio (w/c), aggregate grain size distribution, fly ash, and water-reducing agent. An increase in compressive strength of approximately 5 MPa can be obtained if 100 x 200 mm cylinders are rodded in four layers, 25 rods each, if the slump is not over 100 mm. For all other mixtures, the current rodding procedure of two layers, 25 rods each, is recommended. For mixtures with higher slump, two layers with less rodding per layer deliver similar strength values, but the variability is high.

This study focuses on enhancing the durability of two-component grouting materials by incorporating ground-granulated blast- furnace slag (GGBFS) and replacing cement with industrial waste to reduce environmental pollution. A ternary cementitious system was developed using 30% GGBFS and 10% carbide slag (CS) as partial cement replacements. The research investigates the effects of different water-bentonite ratios, water-binder ratios (w/b), and A/B component volume ratios on the physical and mechanical properties of the grout, including density, fluidity, bleeding rate, setting time, and strength performance. The microstructural evolution and hydration products were analyzed using scanning electron microscopy (SEM), X-ray diffraction (XRD), mercury intrusion porosimetry (MIP), and thermogravimetric analysis (TGA). The findings provide insights for optimizing the mixture design of grouting materials in shield-tunneling applications, with a focus on improving performance and sustainability.