Nano-Scale Behavior and Nano-Modification of Cement and Concrete Materials

Introduction

Cement and concrete are the most widely used construction materials because they are resistant to water, easily formed into various shapes and sizes, the cheapest and readily available everywhere. In the foreseeable future, cement and concrete materials will continue to play an important role in construction materials. However, the development of cement and concrete materials is encountering enormous problems and challenges. Firstly, cement manufacturing consumes high energy and spits out a large amount of carbon dioxide. Additionally, most raw materials of cement are non-renewable. These disadvantages mentioned above are likely to pose great pressure on environment. Secondly, increasing attention has been paid on the security of cement and concrete structures since cement and concrete are brittle materials and usually work with cracks. Thirdly, the durability of cement and concrete structures is a very important issue, in particular during the process of their design and application. Fourthly, cement and concrete materials are complex composites in nature. There are difficulties in how to bring about huge revolution in the cement and concrete material field unless it is available to have a good understanding of cement hydration process, main hydrate phases and so on. Fifthly, the multifunctional and smart cement and concrete materials are required since traditional cement and concrete that just serve as structural materials can not meet the requirement of construction of advanced engineering structures.

Nanotechnology is an emerging field related to the understanding and control of matters at nanoscale. Some remarkably specific properties and functions are exhibited when materials reach nano-size. Recent developments of nanotechnology show significant promise in addressing many of the challenges in various areas. To date, applications and advances of nanotechnology have injected new vitality into cement and concrete materials (Bartos, 2009). The vitality mainly reflects in understanding more about behaviors of cement and concrete materials at nano-scale, fabricating nano-cement and modifying cement and concrete materials by addition of nano-materials. The main advance is that we can learn about basic phenomena in cement at nano-scale (Bartos, 2009; Scrivener & Kirkpatrick, 2008). Jo et al. (2014) used the bead milling to produce ultrafine cement (~220 nm) without changing the chemical phase. The application of nanotechnology makes cement and concrete materials have high mechanical properties, high durability, and even multifunctionility. Li et al. (2004) studied the impact of addition of 3 wt. %, 5 wt. % and 10 wt. % of nano-silica (NS) to cement mortars, and achieved an increase in compressive and flexural strengths. Haruehansapong et al. (2014) fabricated cement mortars containing different contents (3%, 6%, 9% and 12% of cement weight) of NS with various sizes of 12 nm, 20 nm and 40 nm. They observed that 40 nm NS is more effective for improving compressive strengths compared with 12 nm and 40 nm NS. The optimum content of 9% NS can improve compressive strength to 1.5 times at 28 d against the plain cement mortars. Li (2004) incorporated 4% NS into concrete with 50 wt. % fly ash and obtained an increase of 81% in compressive strengths compared with concrete with only 50 wt. % fly ash at 3 d. Using of NS shows a new approach to save cement so that the pressure on environment can be reduced. Oltulu et al. (2014) found that NS can refine pore structure of hardened cement and concrete materials. Apart from NS, nano-TiO₂ (NT) and nano carbon materials (NCMs) were also used to modify cement and concrete materials. Cement and concrete materials filled with NT have the function of decomposing environment pollution, self-cleaning and self-disinfecting (Chen & Poon, 2009). Sáez De Ibarra et al. (2006) reinforced cement paste by using carbon nanotubes (CNTs). They found addition of only 0.1 wt. % of CNTs can increase hardness by 177% and Young’s modules by 227%. Besides mechanical properties, NCMs can endow cement and concrete with thermal property, sensing property, electromagnetic interference property and other properties (Han et al., 2015). Some researchers have also studied the properties of cement and concrete materials with other nano-materials, such as nano-fly ash, nano-Al₂O₃ (NA), nano-Fe₂O₃, nano-ZnO₂, nano-CuO, nano-Cu₂O₃, nano-ZrO₂, nano-CaCO₃ (NC) and nano-clay.