The potential pozzolanic activity of glass and red-clay ceramic waste as cement mortars components

Abstract

The objective of this experimental study was to examine the possibility of reusing ceramic materials waste from container glass, bricks and tiles of red-clay ceramic industry in Portugal as partial cement replacement in mortar and concrete. The different types of waste were finely ground to specific sizes (0–45 μm, 45–75 μm and 75–150 μm) and its pozzolanic activity was determined. The reduction of glass and ceramic waste particle size was accomplished in the laboratory by crushing and grinding using a ball jar mill. After gridding, the fine waste materials were characterized by the determination of density, Blaine fineness and particle morphology using scanning electrical microscope. The compressive strength activity index, at 7, 28 and 90 days, was determined in mortars produced with each finely grounded waste ceramics and different percentages of partial cement replacement. Standard ASTM accelerated mortar bar tests and a modified test carried on in 40 × 40 × 160 mm size mortar specimens were performed to investigate the potential expansion caused by the alkali–silica reaction of finely grounded waste glass as partially cement replacement.

The results obtained confirm the pozzolanic activity of the grounded waste, collected in the central region of Portugal, making feasible their incorporation as cement mortars and concrete components.

Introduction

The mechanical and durability related properties of cement mortar and concrete can be enhanced by the incorporation of minerals admixtures. When such minerals admixtures come from industrial by-products, its reuse contributes to reduce CO₂ and other greenhouse gases emissions due to production, also contributing to the reduction of the potential environmental impacts caused by landfill deposit.

In Portugal, non-recyclable waste glass constitutes a problem for solid waste disposal in different local regions. Traditionally, most non-recyclable mixed-colour broken glass is coming from the bottling industry. The current waste management practice is still to landfill deposit most of the non-recyclable glass. Since glass is not biodegradable, deposit in landfills do not provide an environment-friendly solution. At the same time, in Portugal, the available pozzolanic materials for cement and concrete production will soon be insufficient to supply all the demands of the construction industry. Nowadays, the civil construction industry is searching for alternatives to satisfy the increasing needs for cement and concrete production.

In Portugal, disposed used glass bottles are only partially reutilized as new products. They are collected, sorted, and crushed to be used mostly as a raw material for new bottles. However it is estimated, according to relatively recent data, that only 30% of the total disposed used bottles are actually currently being recycled [1].

According to Eurostat and Eionet in 2001, the generation of glass waste was of 493 thousand tonnes and only 25% of this was recycled. Currently, in 2008, accordingly FEVE – the European Container Glass Federation this percentage of recycling has increased in Portugal, up to 52%.

Efforts have been made in the concrete industry to use glass waste as partial replacement of coarse or fine aggregates. However, due to the strong reaction between the alkali in cement and the reactive silica in glass (ASR reaction), studies of the use of glass in concrete as part of the coarse aggregate were not always satisfactory due to considerable strength reduction by simultaneously occuring expansion [2], [3]. Shi and Zheng [4] have revealed that despite the traditional alkali–silica reaction theories used to explain the expansion of cement concrete containing mixed glasses waste as aggregates, the expansion phenomena are different from those of conventional alkali–silica reaction caused by certain aggregates types. Figg [5] has noticed, as well, some differences between alkali–silica reaction expansion caused by natural aggregates and expansion caused by glass aggregate.

Recent studies have shown that the particle size of glass is a crucial factor for alkali–silica reaction (ARS) to occur [6]. In particular, aggregate fineness favours ASR expansion is a surface area dependent phenomenon. It seems that there is a minimum particle size, depending on the structure of the glass, where the maximum expansion occurs. Thus, it was found that if the glass was ground to a particle size of 300 μm or smaller, the ASR induced expansion could be reduced [7]. In fact, data reported in the literature show that if the waste glass is finely ground, under 75 μm, this effect does not occur and structural integrity of mortar containing fine glass is guaranteed [2].

It is also well known that typical pozzolanic materials might feature high silica content, an amorphous structure and have a large surface area.

The industrial red-clay ceramic products waste, such as bricks and tiles have been investigated for alternative cementitious materials [8], [9], [10], [11]. Comparing the cement mortars behaviour without and with the incorporation of ground calcined-clay brick and metakaolin, it was observed an increase in total porosity and a reduction in strength with the increasing of the cement replacement by ground calcined-clay brick [12]. However, up to 20% replacements compressive strengths obtained at 90 days are of the same order or greater than those obtained with a plain cement control mix [13]. Moreover, a good degree of hydraulicity of the mortar is dependent of powder fineness and bricks firing temperatures [14].

Thus, taking into consideration such results, the main objective of this study was to evaluate the potential pozzolanic activity of glass waste of different colours types and red-clay ceramic waste from materials produced with different kiln temperatures. The results obtained have been compared with those of reference mortar to observe the effect of waste volume increasing as partial cement replacement, the effect of oxides and other compounds used as glass pigments as well as the effect of the kiln temperature to produce red-clay ceramic materials on the pozzolanic reactivity. The effect of five different amounts of glass in three different colours was also determined in terms of ARS using two different methods.