Ultra-high-performance concrete (UHPC) can be vulnerable to variations in materials properties and environmental conditions. In this paper, the sensitivity of UHPC to changes in mixing, casting, curing, and testing temperatures ranging between 10 and 30 ± 2°C (50 and 86 ± 3.5°F) was investigated. The investigated rheological properties, mechanical properties, and shrinkage of UHPC are shown to be significantly affected by temperature changes. UHPC made with either binary or ternary binder containing fly ash (FA) or slag cement exhibited greater robustness than mixtures prepared with 25% silica fume. UHPC made with 60% FA necessitated the lowest high-range water-reducing admixture demand. With temperature increase, the yield stress of UHPC mixtures increased by up to 55%, and plastic viscosity decreased by up to 45%. This resulted in accelerating initial and final setting times by up to 4.5 and 5 hours, respectively. The increase of temperature from 10 to 30 ± 2°C (50 ± to 86 ± 3.5°F) led to a 10 to 75% increase in compressive, splitting tensile, and flexural strengths and modulus of elasticity and 15 to 60% increase in autogenous shrinkage.

The objective of this study was to evaluate the effectiveness of colloidal nanosilica (nS) as a nanomaterial and pozzolanic admixture to mitigate the deteriorative effects of sodium sulfate-based physical salt attack (PSA) on portland cement mortars. Mortar mixtures of an ASTM C150 Type II (<8% C3A) or a Type V (<5% C3A) portland cement were prepared with 0, 3, and 6% cement replacements with either nS or microsilica (mS). Test samples were subjected to 3 years of exposure under a constant or cyclic PSA-conducive environment. The PSA results were supported with additional water absorption, rapid sulfate ion permeability (RSPT), and porosimetry testing. The Type V cement mortars containing nS exhibited the most observable scaling and flaking under both conditions of PSA exposure. The addition and increase in cement replacement with nS had a clear detrimental effect to PSA resistance for both cement types and both types of PSA exposure. Results indicated nS reduces permeability and diffusion in mixtures of either cement type which, for PSA, the denser and more refined pore network proved conducive to higher damaging tensile stresses and distress. The larger the measured volume of permeable pore space through absorption, the less susceptible the mortars were to PSA, which is counterproductive to conventional good practice of designing high-durability concrete via reducing permeability and sorption, and increasing a mixture’s watertightness.

This investigation was carried out to develop high-strength cementitious composite mixtures of compressive strength greater than 90 MPa (13.05 ksi). The main aim of this study is to develop high-strength cementitious composites having high density with low void content. To achieve the requirement, cement, copper slag, quartz powder, and silica fume ingredient proportions were arrived by optimum partial packing as well as the Dewar and Larrard method. More than 60 cementitious composite mixtures with and without high-strength micro-steel fiber and chopped basalt fiber were prepared and their compressive strength at the age of 28 days cured under normal water curing was investigated. In all the investigated trial mixtures, 100% copper slag was used instead of normal river sand and a required quantity of high-range water-reducing admixture (HRWRA) was used to maintain workability. Based on the 28-day compressive strength (greater than 90 MPa [13.05 ksi]), four cementitious composite mixtures were selected as optimized mixtures and their mechanical and durability properties were evaluated as per Indian Standard IS 516 and ASTM C469, and their rapid chloride permeability was assessed by ASTM C1202. X-ray diffraction (XRD) and scanning electron microscope (SEM) analysis were also carried out on four optimized composite mixtures. This project aims to develop mixtures suitable for the construction of storage buildings for arms and ammunition of defense research and development organizations (DRDO), and also these composites can be used in many special applications where high mechanical and durability properties are required.

This study aimed to optimize the use of fine and coarse expanded slate lightweight aggregates in developing successful semi-lightweight self-consolidating concrete (SLWSCC) mixtures with densities ranging from 1850 to 2000 kg/m3 (115.5 to 124.9 lb/ft3) and strength of at least 50 MPa (7.25 ksi). All SLWSCC mixtures were developed by replacing either the fine or coarse normal-weight aggregates with expanded slate aggregates. Two additional normal-weight self-consolidating concrete mixtures were developed for comparison. The results indicated that due to the challenge in achieving acceptable self-consolidation, a minimum binder content of at least 500 kg/m3 (31.2 lb/ft3) and a minimum water-binder ratio (w/b) of 0.4 were required to develop successful SLWSCC with expanded slate. The use of metakaolin and fly ash were also found to be necessary to develop successful mixtures with optimized strength, flowability, and stability. The results also showed that SLWSCC mixtures made with expanded slate fine aggregate required more high-range water-reducing admixture than mixtures made with expanded slate coarse aggregate. However, at a given density, mixtures developed with expanded slate fine aggregate generally exhibited better fresh properties in terms of flowability and passing ability, as well as higher strength compared to mixtures developed with expanded slate coarse aggregate.

The study aimed at examining the capacity of diverse add-ons in improving the self-healing ability of fiber-reinforced concrete through low water-cement ratios (w/c) and exposure to wide cracks. The self-healing capacities of crystalline admixture (CA) and silica fume (SF) were assessed by mechanical and durability performance. The effect of various exposure periods (7 to 42 days) in four different exposure conditions—namely, water immersion, wetting-and-drying cycles, water contact, and air exposure (AE)—on self-healing was evaluated by application of through-crack compressive stress. Compressive strength and durability analysis showed that CA with 10% SF was excellent in all four environments. Fourier transform infrared spectroscopy and scanning electron microscope results showed significant bond formation contributing to the self-healing property of the CAs. Therefore, concrete mixture with CA and 10% SF is recommended for use to increase the self-healing of concrete.