International Concrete Abstracts Portal

To prepare the SiO2 aerogel gypsum-based lightweight thermal insulation wall materials with better water resistance, α-hemihydrate gypsum (HG) was used as the main cementitious material. By adding Portland cement (PC), fly ash (FA), and hydrated lime (HL), HG was modified. Using these materials, the HG-PC system and HG-PC-FA-HL system were constructed, respectively. The effects of inorganic admixture content on the performance of both systems were analyzed. Results show that the mechanical properties and water resistance are improved after adding a certain proportion of mineral admixtures to HG. The mechanical properties and water resistance of the HG-PC-FA-HL system are better than the HG-PC system. At the content of 9 wt% FA, 20 wt% PC, and 4 wt% HL, the 28-day strength reaches 41.07 MPa (5955 psi), the water absorption after soaking for 48 h is 12.7 %, and the softening coefficient is 0.72.

The concentration of chloride ions involves both chemical binding and physical adsorption. This study investigated how limestone powder and supplementary cementitious materials (SCMs) synergistically affect chloride concentration in cement paste, using analyses of corrosion products, pore structure, and chloride concentration coefficient. Cement pastes with 0 to 50% limestone powder and fly ash or slag were tested. Results showed that the synergy between limestone powder and fly ash or slag promoted carboaluminate formation, which completely converted to Friedel’s salt in chloride environments. This enhanced chemical binding and increased physical adsorption of chloride ions, while reducing porosity and the most probable pore diameter. When limestone powder was 5 to 25% with fly ash less than 10%, or both limestone powder and slag were 20 to 30%, the chloride concentration coefficient reached its peak. Thus, proper limestone powder content improves chloride resistance by enhancing both chemical and physical chloride binding.

This study investigates the impact of under-sulfated cement combined with high-calcium fly ash and lignosulfonate-based admixtures in ready mixed concrete, leading to rapid stiffening and delayed setting. Using an on-board slump-monitoring system (SMS) installed on a ready mixed concrete truck, significant increases in water demand were recorded to maintain target slumps, with mixtures showing minimal slump response to water additions. Laboratory tests, including isothermal calorimetry and mortar trials, confirmed the under-sulfated cement’s inadequate sulfate levels as the cause. Optimal sulfate addition was determined through calorimetry, and adjustments with gypsum effectively remedied rapid stiffening and delayed setting. This research demonstrates that an SMS can detect undesirable combinations of cement, fly ash, and admixtures in concrete, allowing real-time corrections. It underscores the importance of optimized sulfate levels in cement, particularly when using high-calcium fly ash combined with some high-range water reducers, to achieve desired concrete performance under varying field conditions.

ASTM C31 describes the procedure for making concrete specimens in the field. Its origin can be traced to 1920, proposing rodding or stroking each 100 mm thick layer 25-30 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. Mix design variations include paste volume, w/c, aggregate grain size distribution, fly ash, and plasticizer. An increase in compressive strength of approximately 5 MPa can be obtained if 100 × 200 mm cylinders are rodded in 4 layers, 25 rods each, if the slump is not over 100 mm. For all other mixtures, the current rodding procedure of 2 layers, 25 rods each, is recommended. For mixtures with higher slump, 2 layers with less rodding per layer deliver similar strength values, but the variability is high.

This research establishes a systematic methodology for selectinga migratory corrosion inhibitor (M-CoI) as a repair strategy forreinforced concrete (RC) structures exposed to aggressive environments. Conducted in two phases, Phase 1 involves corrosion testing in pore solutions to evaluate inhibitor efficacy, while Phase 2 examines the percolation ability of M-CoIs in different concrete systems and performance of M-CoI in RC with corroded reinforcing bars. The findings reveal that the efficiency of the compounds as repair measures is significantly lower than their preventive performance, primarily due to the presence of corrosion products onthe steel surface. Additionally, the effectiveness of the M-CoIs isinfluenced by their concentration and form at the reinforcing barlevel; specifically, 4-Aminobenzoic acid (ABA) achieved maximumconcentration in its purest form, whereas Salicylaldehyde (SA) and2-Aminopyridine (AP) reached the reinforcing bar in lower concentrations. Importantly, the study highlights that compounds effective in pore solution may not perform well in concrete, underscoring the necessity of considering the intended application—preventive or repair—when selecting inhibitors. Thus, a comprehensive approach involving both pore solution testing and migration ability assessments is essential for optimal corrosion protection in reinforced concrete.