Effects of light crude oil contamination on the physical and mechanical properties of geopolymer cement mortar

Abstract

Fly ash and oil contaminated sand are considered as the two waste materials that may affect environment. This paper investigated the suitability of producing geopolymer cement mortar using oil contaminated sand. A comparison between physical and mechanical properties of mortar produced using geopolymer and Ordinary Portland Cement (OPC), in terms of porosity, hydration and compressive strength, was conducted. The results showed that heat curing can increase the compressive strength of geopolymer mortar up to 54% compared to ambient curing situation. The geopolymer mortar with 1% of light crude oil contamination yielded a 20% higher compressive strength than OPC mortar containing sand with a saturated surface dry condition. Furthermore, the formation of efflorescence decreased as the level of oil contamination decreased. Moreover, the heat curing method increased the kinetic energy and degree of reaction for geopolymer cement mortar, which cause an increment of the density of the pore system and improving the mechanical properties of the resulting composites. From the results of this study, it was demonstrated that geopolymer mortar has the potential of utilizing oil contaminated sand, and reducing its environmental impacts.

Introduction

There is growing public concern about the wide variety of toxic organic chemicals that are either deliberately or inadvertently being introduced into the environment. Petroleum hydrocarbons are a common example of these chemicals because they enter the environment frequently, in large volumes, and in a variety of ways. Leakage from natural deposits is one of the major ways that crude oil affects the environment [1] Co-produced water associated with the production of oil and gas is also another source of oil contaminated sand [[2], [3], [4]]. Intentionally or accidentally, oil spill contamination has detrimental effects on the properties of the surrounding soil and changes its physical and chemical properties [2]. To minimise its effect on the environment, methods of remediation ranging from sand washing, bio-remediation, electro-kinetic sand remediation, and thermal desorption have been implemented, but are not considered to be cost effective [5]. One alternative method of remediation is using contaminated sand for engineering applications. Some researchers have already investigated the use of sand contaminated with oil in road base materials or topping layers in parking areas [[6], [7], [8]]. Furthermore, several studies investigated how oil contaminated sand would affect the mechanical properties of concrete; for example, how used engine oil affect the properties of fresh, hardened and reinforced concrete [9]. These investigations revealed that the oil acted like a chemical plasticizer and improved the fluidity and doubled the slump of the concrete mix, while maintaining its compressive strength. A similar study was conducted by Mindess and Young [10] where engine oil was added to a fresh concrete mix and found that its effect was similar to adding an air-entraining chemical admixture that enhanced some of the durability properties of concrete. Additionally, the potential use of soil contaminated with petroleum in highway construction was investigated by Hassan et al. [11], and they concluded that it could be used for this purpose. Recent study by Ajagbe et al. [3] investigated the effect of crude oil on compressive strength of concrete, and concluded that 18–90% of its compressive strength was lost due to 2.5–25% contamination with crude oil. Abdul Ahad [12] indicated there was a significant reduction in the compressive strength and about 11% reduction in the splitting-tensile strength of concrete soaked in crude oil.

Geopolymer is a combination of reactive material that is rich in silica and alumina, with alkaline liquid [13]. This material has been studied widely and shown to be a promising green substitute for ordinary Portland cement in some applications. It is reported that geopolymer concrete has good engineering properties [[14], [15], [16], [17]] and it reduces the potential for global warming as a result of its ability to replace ordinary Portland cement [18,19]. Geopolymer concrete was developed as a result of research into heat resistant materials after a series of catastrophic fires [20], and it has the advantage of not using any Portland cement in its production. Geopolymer research has shifted from being in the field of chemistry to engineering applications and commercial production. Furthermore, the use of fly ash has further environmental advantages because the volume of fly ash produced annually is too high compared to the percentage utilised in a beneficial way. For instance in Australia 14.5 million tonnes of fly ash was produced, of which only 2.3 million tonnes were utilised in useful applications, mainly as a partial replacement for Portland cement [17,21]. The improvement of geopolymer technology and applications will lead to a broader utilisation of fly ash, as the use of fly ash in concrete and other building materials has been observed over the last 15 years.

In order to provide a more cost effective solution, oil contaminated sand can be combined with cement binder that come from industrial waste like geopolymer concrete. Currently, most of the studies focused on combining oil contaminated sand with Portland cement in order to provide a better and more cost effective remediation method. However, the effect of crude oil on the properties of geopolymer and cement mortar such as strength, hydration, polarisation, and porosity is still unknown. This study aimed at investigating a new concept for utilizing the contaminated sand in geopolymer concrete which appears to be the first study in this research area.