International Concrete Abstracts Portal

Engineered cementitious composites (ECCs) have excellent toughness and crack-control abilities compared to other cement-based materials, which can be used in underground and hydraulic engineering. Nevertheless, excellent impermeability and workability and low drying shrinkage are also required. Two groups of ECC mixture proportions with high fly ash-cement (FA/c) and watercement ratios (w/c) were chosen as baselines, and silica fume (SF) and a shrinkage-reducing agent (SRA) were introduced to improve the impermeability, workability, and mechanical behaviors. The workability laboratory evaluation indexes of ECC were also discussed. ECC mixture proportions with excellent workability (pumpability and sprayability), high toughness (ultimate tensile strain ɛtp over 3.5%), good impermeability (permeability coefficient K = 1.713 × 10–11 m/s), and low drying shrinkage (drying shrinkage strain ɛst = 603.6 × 10–6) were finally obtained. Then, flexural and shear tests were carried out for the material flexural/ shear strength and toughness evaluations, giving the characteristic material properties for the final ECC mixture proportions.

This study uses neutron radiography (NR) and visual inspection to quantify water penetration in concrete samples exposed to water pressure on one face. It provides experimental data regarding the impact of mixture proportions on the hydraulic permeability of concrete. Specifically, it illustrates the influence of water-cement ratio (w/c), curing duration, entrained air content, and coarse aggregate (CA) size and volume on water transport. In addition, this paper quantifies the impact of permeability-reducing admixtures (PRAs) on water transport in concrete. It was observed that decreasing the w/c and/or increasing the curing duration reduced the fluid transport. Liquid and powder PRAs efficiently reduced fluid transport in concrete without impacting the compressive strength. The liquid PRA showed more consistent results, likely due to better dispersion than the powder PRA. Fluid ingress in concrete samples appears to increase with entrained air content due to a lower degree of saturation (DOS) at the start of the test. Increasing the CA volume fraction or decreasing the CA size will increase the fluid transport in concrete due to an increase in the connectivity of the interfacial transition zone. The influence of entrained air content, curing duration, CA volume fraction, and CA size was less noticeable on mixtures with PRAs due to the higher density and low permeability of these samples compared to control samples.

The objective of this paper is to investigate the microscopic pore characteristics and macroscopic mechanical properties of concrete under different curing conditions. Ultrasonic nondestructive testing technology was used to measure the ultrasonic sound velocity of specimens of different ages, and the compressive strength and splitting tensile strength were obtained through indoor mechanical performance tests. The pore-size distribution characteristics and internal microstructure were observed using nuclear magnetic resonance (NMR) technology and scanning electron microscopy (SEM) testing, respectively. The results revealed that, compared with standard curing conditions, the decrease of the curing temperature and humidity can result in the volume and proportion of macropores and microcracks being larger, which results in the deceleration of the ultrasonic wave speed inside the concrete and the decrease of the mechanical properties. Under the same curing condition, a lower water-binder ratio (w/b) enables the internal pore surface area of the material to increase, and the mechanical properties are improved. With the decrease of the curing temperature and relative humidity, the stress-strain curve appeared delayed in the initial compaction stage and presents more obvious brittleness characteristics in the failure stage. By fitting the relationship between the concrete strength and the porosity under different curing conditions, an extended model that can be applied to cement-based materials was obtained. Additionally, it was found that the porosity is negatively correlated with the ratio of the compressive strength to splitting tensile strength of the concrete.

The reactions of supplementary cementitious materials (SCMs) in concrete can be pozzolanic, hydraulic, or a combination of both. This paper focuses on the pozzolanic reactivity test (PRT) for SCMs that are blends of reactive aluminous and siliceous phases. The PRT quantifies reactivity by measuring heat release (Q) and calcium hydroxide (CH) consumption, which are interpreted using thermodynamic modeling. The robustness of the PRT is examined by experimentally varying the CH-to-SCM ratio, solution-to-solid ratio, sulfate content, alkali type (Na versus K), and alkali content. This paper also assesses similarities and differences between the PRT and the R3 test (ASTM C1897). It was found that sulfates, which are used in the R3 test, did not impact the siliceous reactions; however, they led to the preferential reaction with aluminous phases to form monosulfoaluminates and ettringite. A generalized relationship for the degree of reactivity is proposed as a function of Q and CH consumption.

Six deep beams without transversal reinforcement made of sand-lightweight concrete and six deep beams made of sand-lightweight concrete with 1.0% of steel fibers were tested and compared with conventional concrete deep beams with and without fibers. The shear-span to deep beam height ratio (a/h) was 0.5, 0.8, and 1.0. The cross section heights were 400, 600, and 700 mm (15.7, 23.6, and 27.6 in.). The deep beams were tested to failure under a four-point bending test, using a hydraulic actuator with 500 kN (674 kip) capacity load cell. After testing, it was concluded that the shear-strength values were smaller in larger span deep beams. The presence of steel fibers increased the maximum strength and contributed quantify to the strength to diagonal cracking. The maximum shear load in steel fiber deep beams increased by approximately 16%. The size effect was more significant in sand-lightweight concrete deep beams. Besides, it was proposed a coefficient to validate the cracking strut-and-tie model (CSTM) to evaluate the applicability in deep beams of sand-lightweight concrete with and without steel fibers and the experimental maximum shear predictions are compared according to some codes for sand-lightweight concrete deep beams and by codes and some codes and researchers for sand lightweight concrete deep beams with steel fibers.