Influence of aggregate source and size on the shear behavior of high strength reinforced concrete deep beams

This paper aims to examine the influence of coarse aggregate characteristics, including toughness and nominal maximum size of aggregate on the RC deep beams’ shear behavior made with and without shear reinforcement. Nine deep beams were prepared with three coarse aggregate types (i.e., limestone, steel slag, and quartzite) having different toughness properties and two nominal maximum aggregate (10 mm and 20 mm) sizes, which were examined under four-point bending. The experimental findings showed that the deep beams exhibited shear failure caused by diagonal shear cracks initiated between the supports and the loading point. Utilizing bigger coarse aggregate size has led to reducing the number of shear cracks. The deep beam stiffness was not impacted by the change in coarse aggregate toughness, aggregate size, or the use of shear reinforcement. For the beams without shear reinforcement, increasing the nominal maximum coarse aggregate size improved the deep beams normalized shear strength. This improvement depended on the coarse aggregate’s toughness with the toughest aggregate (steel slag) showing the greatest improvement. Moreover, using shear reinforcement has contributed to improving the deep beams’ normalized shear strength. The normalized shear strength increased from 6% to 16% compared to deep beams without shear reinforcement

Concrete Performance Produced Using Recycled Construction and By-Product Industrial Waste Coarse Aggregates

Concrete is classified as a multi-composite material comprising three phases: coarse aggregate, mortar, and interfacial transition zone (ITZ). Fine and coarse aggregates occupy approximately 70–85% by volume, of which coarse aggregate typically constitutes more than two-thirds of the total quantity of aggregate by volume. The current study investigates the concrete performance produced using various recycled construction and by-product industrial waste coarse aggregates. Six types of coarse aggregates: manufactured limestone, quartzite, natural scoria, by-product industrial waste aggregate, and two sources of recycled concrete aggregates with densities ranging from 860 to 2300 kg/m3 and with different strength properties were studied. To determine the coarse aggregate contribution to the overall concrete performance, lean and rich concrete mixtures (Mix 1 and Mix 2) were used. Mix 1 (lean mixture) consisted of a ratio of water to cement (w/c) of 0.5 and cement content of 300 kg/m3, whereas a higher quantity of cement of 500 kg/m3 and a lower w/c ratio of 0.3 were used for Mix 2 (rich mixture). The results showed that while the compressive strength for different aggregate types in Mix 1 was comparable, the contribution of aggregate to concrete performance was very significant for Mix 2. Heavyweight aggregate produced the highest strength, while the lightweight and recycled aggregates resulted in lower mechanical properties compared to normal weight aggregates. The modulus of elasticity was also substantially affected by the coarse aggregate characteristics and even for Mix 1. The ACI 363R-92 and CSA A23.3-04 appeared to have the best model for predicting the modulus of elasticity, followed by the ACI-318-19 (density-based formula) and AS-3600-09. The density of coarse aggregate, and hence concrete, greatly influenced the mechanical properties of concrete. The water absorption percentage for the concrete produced from various types of aggregates was found to be higher for the aggregates of higher absorption capacity

Lightweight SCC Development in a Low-Carbon Cementitious System for Structural Applications

The utilization of manufactured lightweight aggregates adds another dimension to the cost of the preparation of self-compacting concrete (SCC). The common practice of adding absorption water to the lightweight aggregates before concreting leads to inaccurate calculations of the water-to-cement ratio. Moreover, the absorption of water weakens this interfacial bond between aggregates and the cementitious matrix. A particular type of black volcanic rock with a vesicular texture known as scoria rocks (SR) is utilized. With an adapted sequence of additions, the occurrence of water absorption can be minimized to overcome the issue of calculating the true water content. In this study, the approach of preparing the cementitious paste first with adjusted rheology followed by the addition of fine and coarse SR aggregates enabled us to circumvent the need for adding absorption water to the aggregates. This step has improved the overall strength due to the enhanced bond between the aggregate and the cementitious matrix, rendering a lightweight SCC mix with a target compressive strength of 40 MPa at 28 days, which makes it appropriate for structural applications. Different mixes were prepared and optimized for the best cementitious system that achieved the goal of this study. The optimized quaternary cementitious system included silica fume, class F fly ash, and limestone dust as essential ingredients for low-carbon footprint concrete. The rheological properties and parameters of the optimized mix were tested, evaluated, and compared to a control mix prepared using normal-weight aggregates. The results showed that the optimized quaternary mix satisfied both fresh and hardened properties. Slump flow, T50, J-ring flow, and average V-funnel flow time were in the ranges of 790–800 mm, 3.78–5.67 s, 750–780 mm, and 9.17 s, respectively. Moreover, the equilibrium density was in the range of 1770–1800 kg/m3. After 28 days an average compressive strength of 42.7 MPa, a corresponding flexural load of over 2000 N, and a modulus of rupture of 6.2 MPa were obtained. The conclusion is then drawn that altering the sequence of mixing ingredients becomes a mandatory process with scoria aggregates to obtain high-quality lightweight concrete for structural applications. This process leads to a significant improvement in the precise control of the fresh and hardened properties, which was unachievable with the normal practice used with lightweight concrete