Physical, mechanical and microscopic investigation on self-cured concrete containing Green Artificial Aggregate (GAA)

Lightweight aggregates replacing natural aggregate act as internal water reservoirs, mitigating shrinkage, improving hydration, and reducing evaporation while addressing environmental and economic challenges of water-intensive curing. However, there is limited study available on using Green Artificial Aggregate (GAA), a sustainable lightweight aggregate manufactured from waste material specifically ceramic waste, bottom ash and fly ash as self-curing agent in concrete. The present study aims to examine the potential of GAA as a self-curing agent in concrete while evaluating its effects on strength and durability performance compared to conventional concrete with curing and without curing process. The Design of Experiments (DOE) method was adopted for the mix design to produce concrete Grade 30 with the water cement ratio used was 0.53. The aggregates condition used in the concrete mixes was divided into air-dry (AD) and saturated-surface-dry (SSD). Two types of curing regimes were used namely water- curing and air-curing. Normal concrete was also prepared as a control specimen. Various tests were carried out to determine the characteristics of the aggregates including specific gravity, water absorption, water desorption, surface texture, aggregate crushing value, porosity, x-ray fluorescence and sieve analysis. The performance of self-cured concrete was determined through compressive strength, ultrasonic-pulse velocity, density, flexural strength, modified compressive strength, shrinkage, expansion and initial surface absorption. Furthermore, various techniques including scanning electron microscopy (SEM) with energy dispersive X-ray (EDX) Analysis, X-ray diffraction (XRD) and mercury intrusion porosimetry (MIP) were used to study the microstructure of the self-cured concrete. The experimental results showed that that GAA possesses significantly higher water absorption (10.6%) compared to granite (0.32%), enabling it to function effectively as an internal water reservoir. Control concrete exhibited superior compressive strength, though self-cured concrete demonstrated enhanced strength development. The performance differential between control and GAA concrete is attributed to GAA's porosity. Statistical analyses confirmed aggregate type and curing regimes significantly influence mechanical properties. GAA's porosity facilitates internal water reservation for hydration. SSD and AD GAA showed comparable compressive strength, indicating pre-soaking is unnecessary for effective internal curing. Self-cured specimens performed optimally with delayed demoulding under air-curing, while conventional concrete maximized strength with early demoulding in water-curing. Statistical analyses revealed demoulding timing negligibly affects compressive strength, suggesting expedited formwork removal enhances construction efficiency without compromising structural integrity. Microstructural analysis revealed elevated calcium concentrations in self-cured concrete relative to controls indicate enhanced hydration, improved C-S-H formation, and denser microstructure from internal curing. SSD GAA concrete exhibited superior pore refinement notably a 27% diameter reduction in air-cured specimens enhancing durability and reducing permeability. Overall test results together with microstructure study showed that GAA can be used as self-curing agent in the concrete. This research contributes to United Nations Sustainable Development Goals (UN SDGs) 9, 11, 12, and 13 by transforming industrial and construction waste into valuable construction materials, thereby reducing water consumption and natural resource extraction while promoting sustainable infrastructure and climate action.