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

Current methods for producing self-compacting concrete (SCC) using lightweight aggregates face challenges in water-to-cement ratio accuracy and interfacial bonding. Traditional approaches involve pre-soaking aggregates, which introduces uncertainty in water content and weakens the bond between aggregates and cement. This gap motivated researchers to explore alternative mixing sequences and materials to enhance both fresh and hardened properties. Prior research has shown that absorption water affects workability and strength. However, no prior work had resolved the issue of precise water control in lightweight SCC. The need for structural applications with high compressive strength and low carbon footprint remains unmet. Existing literature lacks a systematic approach to optimize quaternary cementitious systems for lightweight SCC. This paper contributes by proposing a new method to bypass absorption water requirements. The study also introduces a low-carbon cementitious system using industrial byproducts. The novelty lies in the adapted sequence of additions to improve bond strength and control water content.

This study aimed to develop a lightweight SCC mix with structural-grade compressive strength while minimizing the carbon footprint. The specific problem addressed is the inaccuracy in water-to-cement ratio calculations due to aggregate absorption. The motivation stems from the need for reliable and sustainable construction materials. Researchers sought to improve bond strength between aggregates and cement by altering the mixing sequence. They also aimed to optimize a quaternary cementitious system using low-carbon materials. The goal was to achieve 40 MPa compressive strength at 28 days. The study tested the feasibility of using scoria rock as a lightweight aggregate. The approach involved preparing cement paste first before adding aggregates. This method was expected to eliminate the need for absorption water. The results were compared to a control mix using normal-weight aggregates.

The study utilized scoria rock, a black volcanic material with a vesicular texture, as the lightweight aggregate. Researchers first prepared a cementitious paste with adjusted rheology before adding fine and coarse SR aggregates. This sequence avoided the need for absorption water. The quaternary cementitious system included silica fume, class F fly ash, and limestone dust. These materials were selected for their low-carbon properties. The optimized mix was tested for rheological properties such as slump flow, T50, J-ring flow, and V-funnel flow time. Hardened properties like compressive strength and modulus of rupture were also evaluated. A control mix using normal-weight aggregates was prepared for comparison. The study measured equilibrium density and flexural load capacity. All parameters were compared against standard SCC requirements. The mixing sequence and material proportions were adjusted to meet structural performance goals. The focus was on achieving precise control of both fresh and hardened properties.

The optimized quaternary mix achieved a slump flow of 790-800 mm, T50 of 3.78-5.67 s, J-ring flow of 750-780 mm, and V-funnel flow time of 9.17 s. These values indicate good workability and flowability. The equilibrium density ranged from 1770-1800 kg/m³, meeting lightweight SCC criteria. After 28 days, the compressive strength averaged 42.7 MPa, exceeding the target of 40 MPa. The flexural load was over 2000 N, and the modulus of rupture was 6.2 MPa. These results suggest strong structural performance. The mix satisfied both fresh and hardened property requirements. The control mix using normal-weight aggregates did not match these results. The adapted mixing sequence improved the bond between aggregates and cement. The study confirmed that altering the sequence is essential for high-quality lightweight SCC. The use of low-carbon materials did not compromise strength or workability.

The study concluded that altering the sequence of mixing ingredients is essential when using scoria aggregates. This approach enables precise control of both fresh and hardened properties. The optimized quaternary system achieved 42.7 MPa compressive strength at 28 days. The method eliminated the need for absorption water, improving bond strength. The results suggest that the adapted sequence is mandatory for high-quality lightweight SCC. The study demonstrated that low-carbon materials can be used without compromising structural performance. The quaternary system included silica fume, class F fly ash, and limestone dust. These materials contributed to the mix's sustainability. The findings support the use of scoria rock as a viable lightweight aggregate. The method offers a practical solution for structural applications requiring SCC. The results were consistent with the study's objectives. The approach provides a reliable alternative to traditional lightweight concrete methods.