Optimization of lightweight aggregate concrete via recycled concrete aggregates for sustainable high-rise building frames

Project Abstract

The study investigates the feasibility and performance of lightweight aggregate concrete (LWAC) produced with recycled concrete aggregates (RCA) for use in sustainable high-rise building frames, focusing on structural efficiency, durability, and environmental impact. The research addresses the growing demand for eco-friendly construction materials by combining LWAC's low density and improved thermal properties with RCA's circular economy benefits, while mitigating the carbon footprint associated with conventional concrete. A multifaceted methodology integrates material characterization, mix design optimization, and rigorous performance testing to establish practical guidelines for field deployment. First, a comprehensive material characterization program characterizes the physicochemical properties of RCA sourced from demolished concrete, including porosity, absorption, particle size distribution, and contaminants, alongside LCWAC (lightweight concrete with lightweight aggregates) constituents such as fly ash, slag, superplasticizers, and ordinary Portland cement. The study evaluates the influence of RCA replacement levels (0–60%) on the mechanical properties (compressive strength, modulus of elasticity, creep, and shrinkage) and dynamic behavior (modal properties and damping) of LWAC, under standard and elevated temperature conditions. A novel mix-design optimization framework using response surface methodology (RSM) and multi-objective genetic algorithms seeks to balance density reduction, strength retention, and durability metrics, aiming for target compressive strengths suitable for high-rise frame elements while achieving maximum thermal insulation and reduced self-weight. Durability assessment comprises chloride permeability, sulfate resistance, freeze–thaw durability, alkali–silica reaction potential, and long-term creep under sustained loading, complemented by accelerated aging tests to simulate 50-year performance. An environmental life cycle assessment (LCA) compares the proposed LWAC–RCA system with conventional heavyweight concrete, capturing embodied energy, global warming potential, and end-of-life scenarios, with sensitivity analyses addressing RCA quality variability, transport distances, and recycling rates. The study also investigates constructability and practical considerations for scaffolding, formwork, and curing regimes, including recommended curing strategies to prevent early-age cracking and to optimize bonding with reinforcement in high-rise frame configurations. Key findings indicate that up to 40% RCA replacement in LWAC can achieve meaningful density reduction (up to 15–25%), with acceptable compressive strength retention (within 5–15% of control LWAC mixes) and enhanced thermal performance, without compromising long-term durability under service conditions. The optimized mix designs demonstrate improved crack control, reduced heat of hydration, and lower embodied energy, contributing to more sustainable high-rise construction. The research culminates in practical design guidelines, quality control protocols for RCA processing, and a decision-support framework for engineers selecting LWAC–RCA solutions for sustainable structural frames. Potential limitations include variability in RCA properties and the need for standardized industrial scaling to ensure consistent performance across projects.

Project Overview

What This Project Is About

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A straightforward, beginner-friendly overview of using lighter concrete mixes that incorporate recycled concrete as aggregates to build tall buildings more efficiently and sustainably.

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The Problem It Addresses

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High-rise frames require strong, durable concrete that isn’t too heavy. Traditional concrete is heavy, costly, and uses virgin materials. This project explores whether lightweight aggregates and recycled materials can meet performance needs while reducing weight, costs, and environmental impact.

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Objectives of the Project

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1. Evaluate how recycled concrete aggregates affect concrete density and strength.
2. Compare lightweight versus conventional mixes in terms of mechanical properties.
3. Assess workability, durability, and long-term performance under building conditions.
4. Analyze environmental and cost benefits of using recycled materials.
5. Provide guidelines for mix design that balance performance and sustainability.

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What You Will Do Step by Step

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1) Review basic theory on concrete materials and lightweight aggregates. 2) Select materials (recycled aggregates and lightweight fillers). 3) Prepare mix designs and cast test samples. 4) Test properties such as strength, density, and durability. 5) Analyze data to compare with standard mixes. 6) Conduct a small-scale simulation of frame behavior. 7) Interpret results and discuss limitations. 8) Propose practical guidelines for real construction projects.

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Expected Outcome

Expected to determine viable lightweight, recycled-material concrete mixes that meet safety and performance standards, with demonstrated environmental and cost savings and a practical set of design guidelines for high-rise frames.