Lightweight Concrete with Expanded Glass

As the single most widely used construction material in the world with a carbon footprint to equal it, concrete is of substantial interest in relation to sustainable development; there are many environmental consequences induced by the consumption of raw materials and processing operations for the production of building materials and disposal of construction wastes.

There are, however, interesting opportunities of recycling waste materials as well that can improve its sustainability. Often, structural lightweight concrete is obtained by replacing part of the ordinary aggregate with lightweight aggregate particles. Many of these materials, such as tuff, pumice, and clay are not cost-effective, efficient, or readily available. Waste glass, however, is an interesting possibility as it is widely available worldwide and that, after being ground to achieve particle size distributions comparable to those of common cements, waste glass can be used as a mineral addition.

This paper 1) describes an experimental study aimed at developing a structural lightweight concrete with expanded glass particles and silica fume that is suitable for structural applications and; 2) evaluates microstructural changes in wet conditions and resistance to the action of aggressive ions in the expanded glass particles.

Waste glass is an interesting possibility because this material is widely available worldwide, especially in the finer fraction, which cannot be recycled for usual glass application. The use of glass in concrete, however, arises durability concern because of its poor stability in alkaline environments. For the study, expanded glass particles are characterized in terms of alkali-aggregate reaction, density, absorption, and microstructure.

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Figure 1. Particle size distribution of the ordinary aggregate and expanded waste glass aggregate.

Ordinary river aggregate and a commercial expanded glass aggregate with particles size in the range of 2-4 mm (0.079-0.157 in) were used to prepare mortar samples for testing. Particle size distribution is presented in Figure 1. The aggregate was obtained by mixing 70% by volume of the ordinary aggregate and 30% by volume of the expanded glass.

The aggregates were characterized by bulk density, particle density and water absorption. Mortar (concrete) samples were characterized by slump, air content, and wet density. Compressive strength tests were conducted after immersion in water at 20°C and 40°C (68 and 104°F) for 3, 6 and 9 months to identify long-term stability of the expanded glass aggregate in concrete. Aggregate particles and mortar samples were examined with an environmental scanning electron microscopy. Other tests included dynamic elastic modulus in accordance with RILEM NDT 1, water absorption, drying shrinkage, electrical resistivity, resistance to the penetration of chlorides in accordance with Nordtest NT-BUILD-492, susceptibility of the aggregates to alkali-silica reaction in accordance with ASTM C1260, and resistance to sulfate attack in accordance with ASTM C1012. All tests were carried out on 2-3 replicate specimens.

The results described in this work showed the possibility of using expanded glass aggregates to obtain a structural lightweight concrete with a specified density and compressive strength. Tests indicated that a combination of expanded glass and silica fume led to a structural lightweight concrete that maintained its strength under exposure to moist and hot conditions, while showing high resistance to penetration of aggressive agents.

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