Paper Example on Concrete: The Most Durable Construction Material for Buildings

Chapter One1. Introduction

Concrete is the most commonly used material in the construction industry since its discovery. It has been widely used in most construction projects all over the world as compared to other construction materials such as wood, aluminium, steel, or plastics. The extensive use of concrete is because of its high compressive strength, durability, and workability. The durability of concrete is a critical factor as it determines the life span of the structure. The durability of concrete is mostly affected by several aspects, including the quality of materials used, environmental factors, and use of the structure. Environmental factors include the environmental conditions to which concrete is exposed, such as water, chemicals, or physical processes (Benhelal et al., 2013). These factors are the significant environmental aspects that lead to the deterioration of concrete strength and durability. Thus, there is a need to enhance and improve the characteristics of concrete in several ways.

Is your time best spent reading someone else’s essay? Get a 100% original essay FROM A CERTIFIED WRITER!

Save 25%

Some of the most common ways of improving the durability of concrete is reducing the porosity of concrete to minimize the absorption of water and chemical substances. This is mostly done using concrete admixtures and plasticizers, which reduce the pore spaces in concrete, making it waterproof (Ye, Lura, & van Breugel, 2006). As such, nanotechnology involves the addition of nanoparticle admixtures mainly used for the partial replacement of cement to improve the characteristics of concrete. Nanotechnology has positive effects on concrete, and overall improve the quality of structures constructed using nanoparticles (Pacheco-Torgal et al., 2013). Nanotechnology has been widely recognized and adopted by scholars, professionals, and other players in the construction industry, and numerous studies have been conducted to evaluate the benefits and effects of the use of nanoparticles in construction. Various materials, including nano-silica, carbon nanotubes, nano titanium dioxide, and alumina, have become increasingly used in the nanoengineering of concrete due to the advancement of research and technology (Rasin, Abbas, & Kadhim, 2017). Further studies have been conducted by scholars to determine the optimum amounts that can be used for partial replacement of cement to achieve the required properties of concrete for construction purposes (Quercia & Brouwers, 2010). The current study thus will show the effect of Nano silica (SiO2) with a fixed amount of fly ash and silica fume on concrete porosity, compressive strength, and flexural strength.

1.1 Properties of Nanoparticles

Nanotechnology is a pre-existing technology that has been used in many applications in the construction industry. It is a branch of technology that deals with the creation and utilization of functional structures that have been designed from molecular and atomic scales, whose dimensions are in nanometres. The mechanical properties of concrete are mostly affected by the particle size of the constituent materials, ranging from microscale to nanoscale, and the size of the calcium silicate hydrate gel. Calcium silicate gel (C-S-H) has a similar structure to that of clay in addition to a thin layer of solids separated by gel pores that are filled with an interlayer and absorbed water (Jalal et al., 2012). When nanoparticles are used in concrete production, they fill the pores in the cement paste, which makes the concrete denser, solid, and of increased bonding framework. The use of nanoparticles thus significantly improves the mechanical properties, sustainability, and durability of concrete. Nanoparticles are efficient in improving the physical attributes and resilience of high-performance concrete and increases the shear and flexural strength, water resistance, acid resistance, and the self-healing qualities of concrete (Benhelal et al., 2013).

1.2 Concrete

Since its discovery, concrete has been the most common and widely used construction material as compared to other construction materials such as metals, timber, glass, or plastics. Its use, however, comes with shortcomings, as some of the properties of concrete may not reach the required standards or may deteriorate if the structures are not well taken of, increasing the need to find new ways of improving the properties so that the structures remain durable and sustainable (Wahab et al., 2013). Cement supplements such as nano-silica, fly ash, and silica fume have offered the most promising results and have proved their usability for partial replacement of cement (Shekari & Razzaghi, 2011). The inclusion of nano-silica with fly ash and silica fume has been found to reduce the porosity of concrete while maintaining its mechanical properties, reducing and Carbon (IV) Oxide emissions associated with the production of cement, thus reducing environmental degradation.

1.3 Nano-Silica (SiO2)

Nano-silica products are produced in different methods, including the sol-gel process (organic to water route), vaporization of silica between 1500-2000, which reduces quartz silica in an electric arc furnace or by condensation of fine particles in a cyclone. Nano-silica has the highest potential or replacing cement in concrete production. In the production of concrete, nano-silica causes a chemical effect that occurs in the pozzolanic reaction of silica with calcium hydroxide to form the CSH-gel at the final stages (Bianchi & Brouwers, 2010). Due to its smaller size particles as compared to cement particles, nano-silica also has a physical effect on concrete by filling the voids remaining in young and partially hydrated cement paste, which increases the final density of concrete. Presently, nano-silica is mostly applied in the preparation of high performance concretes, self-compacting concretes, and eco-concretes due to its higher price. Nano-silica is applied mostly applied in these concretes because of its anti-bleeding effects, and also because it increases the cohesiveness of concrete, reducing the segregation tendency and porosity (Bianchi & Brouwers, 2010).

1.4 Fly Ash

Fly ash is a component of blended cement or may also be found as a separately batched material that can also be used for partial replacement of cement since it is cost-effective, reduces Carbon (IV) Oxide emissions, and has pozzolanic effects on improving the performance of fresh or hardened concrete. Fly ash is composed of very fine particles which are smaller than cement particles (Arya & Mohamed, 2014). It is also a complex material that consists of heterogeneous amorphous and crystalline phase combinations. Fly ash is also a pozzolanic material since it reacts with lime (CaO) during cement hydration to form a cementitious product. The use of fly ash started in the US in the 1930s. In 1937, R. E. Davis and other scholars at the University of California published results of a research study that they had conducted on concrete containing fly ash. The report documented the specifications, methods for testing the use of fly ash and its applications (Sanchez & Sobolev, 2010).

According to ASTM C618, fly ash can be classified into Class F and Class C according to the amount of alumina, silica, and iron ingredients. Class F fly ash is characterized by more than 70%, while Class C fly ash is characterized by more than 50% and less than 70% of the sum of silica, alumina, and iron ingredients (Jalal et al., 2012). Class F fly ash is generally produced by burning bituminous or anthracite coal or sometimes by burning sub-bituminous coal and lignite. Class C fly ash is generally produced by burning sub-bituminous coal and lignite. Class F fly ash has less Calcium Oxide content as compared to Class C fly ash (Sanchez & Sobolev, 2010).

At an early stage, fly ash has a lower gain of compressive strength since the pozzolanic reaction of fly ash is slower than the heat hydration of cement generated during early ages. However, the gaining of compressive strength is higher after the first 28 days when compared to concrete without fly ash. The durability of concrete can be improved significantly by the addition of fly ash since fly ash reduces porosity and permeability of concrete by making concrete denser. The packing density of concrete and its microstructure of the Interfacial Transition Zone (ITZ) between the cement mortar and aggregate are improved (Mehta, 1986). This improves the overall performance of concrete against extreme conditions such as freezing and thawing, sulfate attack, and chloride penetration in the long term.

1.5 Silica Fume

Silica fume is an industrial by-product that is mainly generated from ferrosilicon producing factories. In its condensed form, silica fume is a very fine, amorphous, and reactive mineral admixture (Givi et al., 2010). Silica fume readily reacts with the calcium hydroxide produced during the hydration of Portland cement. It refines the pore structure of concrete by reducing the volume of pores in concrete, thus increasing its density and mechanical strength. It has a very high specific surface and acts as a reactive pozzolan when used as an admixture in concrete (Mehta, 1986). Normally, it is used in smaller amounts than other pozzolanic materials, and its homogenous dispersion in concrete is difficult, as it may cause the ball bearing effect and localized problems, which can hamper durability problems. This, therefore, calls for the use of small amounts with thorough mixing (Benhelal et al., 2013). Despite the drawbacks, silica fume is a very promising mineral admixture for producing high-performance concrete. However, care must be taken during mixing to avert the problems associated with the proper dispersion of the particles.

1.6 Superplasticizers

Superplasticizers or high-water reducers are improved chemical admixtures over plasticizers and have highly effective plasticizing effects on wet concrete. They result in substantial enhancement on the workability of concrete as a certain water-cement ratio. The use of superplasticizers may achieve a water content reduction of up to 30%. Superplasticizers may be used in higher dosages than conventional plasticizers in the range of 0.5% to 3% by weight of cemen (Quercia & Brouwers, 2010). Some of the superplasticizers are synthetic while others occur naturally and can be classified as follows;

Modified Lignosulphates (MLS)

Sulphonated Naphthalene Formaldehyde Condensate (SNF)

Sulphonated Melamine Formaldehyde Condensate (SMF)

The superplasticizers were developed about three decades ago, but their main drawback in concrete use is slump loss, which can reduce or cancel the advantage of using the superplasticizers, especially in hot weather, reactive elements, and long transportation times of concrete CITATION She11 \l 2057 (Shekari & Razzaghi, 2011).

1.7 Objective and Work Scope

The inclusion of nanotechnology has positive effects...