Hongjian Du

Concrete with Recycled Glass as Fine Aggregates

Recycled waste glasses were used as sand replacement in concrete at 0, 25, 50, 75, and 100% replacement ratios. Diverse concrete properties were tested in fresh and hardened states with three concrete grades; that is, with compressive strengths of 30, 45, and 60 MPa (4350, 6525, and 8700 psi). The incorporation of glass sand showed no significant influence on fresh or mechanical properties of concrete. Drying shrinkage was reduced due to the negligible water absorption of glass sand, especially at lower water-cement ratios (wc). Resistance to chloride ion penetration was substantially enhanced because of the improved and densified microstructure at the interface transition zone (ITZ). Based on alkali-silica reaction (ASR) tests up to 49 days, cement mortar containing glass sand was found to exhibit innocuous expansion. Use of mineral admixtures, such as fly ash and slag cement, could further improve the durability of concrete containing waste glass particles.

Transport Properties of Concrete with Glass Powder as Supplementary Cementitious Material

The study reports a sustainable solution to enhance concrete durability performance by using recycled glass powder as a supplementary cementitious material. Portland cement was replaced at different contents: 15, 30, 45, and 60% by weight. All concrete mixtures containing glass powder showed lower permeability compared to plain concrete. Particularly, 30% was identified as the optimum replacement for glass powder because the highest compressive strength was achieved. For this replacement, chloride diffusion and migration coefficient, water penetration depth, and sorptivity were found to be reduced by 87, 36, 65, and 61%, respectively. The improvements in those transport properties are attributed to the pozzolanic reaction of glass powder, which turned calcium hydroxide into calcium-silicate-hydrates. The microstructure of the formed cement paste and interfacial transition zone is refined and less porous, and therefore more resistant to ingress of harmful fluids and agents.

Sandless concrete with fly ash as supplementary cementing material

As a step towards an environmental friendly and sustainable construction, the properties of concrete made without natural sand (termed sandless concrete herein) and with cement partially replaced with fly ash were investigated. First, the appropriate mixture proportion to ensure the desired properties in sandless concrete for structural applications was established. The effects of coarse aggregate grading, aggregate–cement (A/C) ratio, and water–cement (w/c) ratio on compressive strength were investigated. It was shown that compressive strengths of 30–50u2009MPa could be readily achieved with w/c ratios less than 0.5 and A/C ratios less than 3. Next, the effect of cement replacement by Class-F fly ash by up to 50% on the fresh and hardened properties of sandless concrete was investigated. The incorporation of fly ash improved workability and resulted in higher long-term strength, reduced drying shrinkage, and higher resistance to chloride ingress.

Simulation on the self-compacting concrete by an enhanced lagrangian particle method

The industry has embraced self-compacting concrete (SCC) to overcome deficiencies related to consolidation, improve productivity, and enhance safety and quality. Due to the large deformation at the flowing process of SCC, an enhanced Lagrangian particle-based method, Smoothed Particles Hydrodynamics (SPH) method, though first developed to study astrophysics problems, with its exceptional advantages in solving problems involving fragmentation, coalescence, and violent free surface deformation, is developed in this study to simulate the flow of SCC as a non-Newtonian fluid to achieve stable results with satisfactory convergence properties. Navier-Stokes equations and incompressible mass conservation equations are solved as basics. Cross rheological model is used to simulate the shear stress and strain relationship of SCC. Mirror particle method is used for wall boundaries. The improved SPH method is tested by a typical 2D slump flow problem and also applied to L-box test. The capability and results obtained from this method are discussed.

Towards a sustainable concrete: “sandless” concrete

Abstract As a step towards ensuring the sustainability of concrete as a construction material, an investigation was carried out on the mechanical and durability properties of concrete made without natural sand, termed “sandless” concrete, and with cement partially replaced by fly ash. Four groups of concrete mixes, with water-cement (w/c) ratios of 0.40, 0.45, 0.50 and 0.55, respectively, were studied. For each w/c ratio, there were six mixes with 0, 10%, 20%, 30%, 40% and 50% of cement content replaced by fly ash by mass, and one normal concrete mix containing natural sand. The difference in mechanical properties between normal and “sandless” concrete was not significant. “Sandless” concrete mixes with cement replaced by fly ash by <30% showed comparable compressive, splitting tensile and flexural strengths as those without fly ash. However, the elastic modulus was reduced with the incorporation of fly ash. In addition, use of fly ash led to reduced drying shrinkage of “sandless” concrete, and significantly improved the resistance to chloride ion penetration. The resistance to sulfate attack, on the other hand, seemed to decrease with higher fly ash content. From the study, it appears that “sandless” concrete with cement replaced by fly ash up to 30% could be considered for structural applications.