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the task was a report on the effect of mineral admixtures on cementitious materials. The sample is about a survey on the effect of mineral admixtures on cementitious materials source..
Name Instructor Course Date Effect of Mineral Admixtures on Microstructure of Cementitious Systems 1.0 Introduction Admixtures are included in the concrete to help improve the concrete quality. Some of the notable mineral admixtures include the fly ash (FA), the granulated blast furnace slag (GGBS), the silica fume (SF), metakaolin (MK) and the rice husk ash (RHA). These minerals establish different characteristics that influence the concrete property. The notable advantage of the mineral admixtures is the hardening features exhibited in concrete materials. On the other hand, it is also true that these mineral admixtures can influence the quality nature of wet concrete between the mixing and hardening time. This occurs in one of the following ways; affecting the demand for water, hydration heat, reactivity, setting time and bleeding (Setzer, Rainer Auberg, and Keck 213). Literally, literature that summarizes mineral admixtures influence on the microstructure of cementitious systems. Further, the impact of the mineral admixtures on durability and mechanical properties of concrete is an important point of focus. Besides, the effect of mineral admixtures on concrete properties is vital since the presence of these properties affects the mechanical and durability qualities of concrete (Bartos 126). There are a variety of comparative studies have been undertaken, primarily the effect of blast furnace fly ash and slag when hydrating the fresh cement pastes, impact of the silica fume (SF), the metakaolin (MK), ground granulated blast furnace slag (GGBS) and fly ash during the setting of the high-strength concrete. The aim of this paper is to examine the effect that mineral admixtures have on the microstructure of cementitious systems (Bartos 135). At the same time, the paper makes a distinctive comparative assessment of the mineral admixtures on the hydration heat, water demand, bleeding, setting time and the concrete reactivity. Additionally, the effect of chemical and physical characteristics of silica fume (SF), ground granulated blast furnace slag (GGBS), fly ash (FA), the rice husk ash (RHA) and metakaolin (MK) on the microstructure of cementitious systems (Bartos 201). In this case, therefore, examining C – S – H (Calcium Silicate Hydrate) will be the critical point of examination in this paper. 2.0 Background Coal FA (fuel ash) was first used in concretes in the year 1934. Afterward, based on different research work that was made during the 1950s, several dams were constructed in the United Kingdom by utilizing FA as the partial cementitious material. From this period, these structures have since been exhibiting outstanding conditions (Brebbia and Klemm 233). Pulverized –fuel ash (PFA) or FA obtained from coal materials is a pazzolan that emanates in a low-permeable and durable concrete (Setzer, Rainer Auberg, and Keck 219). This type of concrete can withstand ingress of the deleterious chemical components. Initially, the pazzolan was identified as the controller of the damaging alkali – silica reactions (the ASR) during the year 1949 (Barbero 198). The presence of alkali in the FA concrete is often higher than the cementitious materials lacking the FA (Barbero 206). Hence, this confirms that the presence of FA is important as it protects cementitious materials from ASR effects. Therefore, utilization of FA in concretes has been investigated for a long period and each time, good conditions of the material have been reported. The ground granulated blast furnace slag (GGBS) was first discovered in 1862, and commercial productions started later on in 1865 (Bentur, Arnon, and Kovler 278). The concrete forms that contain GGBS have been identified in a variety of pieces of literature as the slag concrete. This material is being successfully used in different countries as it has many benefits. The SF materials were first obtained during the filtration of exhaust gases from the furnaces in the form of fumes. A great portion of fumes was made up of the fine form of powder with a high silicon dioxide percentage (Brebbia and Klemm 238). Since then, gas filtration has been done on a large scale and during 1976, the first standard of NS 3050 was recommended for use in the factories producing cement. SF is hence, one of the high-quality material used in concrete and cement industry (Kringos 322). Notably, it is stated that adding 8 – 10% by the weight SF in the concrete material; the resulting effect will range between 50, 000 – 100,000 microspheres per cent particles (Bentur, Arnon, and Kovler 293). This implies that the concrete mix becomes highly cohesive and denser because of the presence of the fine particles of SF. MK refers to processed form of amorphous silica components. It is acquired from the calcination of the kaolin at the temperature of 600 – 8500C (Siddique 219). Kaolin materials occur naturally. Its mineralogical and chemical compositions are based largely on the source rock (Tanabe 217). It occurs widely as white clay that results from naturally decomposing feldspar and it is utilized as paper filler, manufacturing of the porcelain materials and textiles as well as an absorbent in the medicines. Lastly, rice husk refers to the outer cover of rice grain characterized by high silica concentration within a range of 80% to 85%. The rice husk makes up 30% of the total weight of the rice kernel. Structurally, it consists of 80% organic components and around 20% non-organic components (Tanabe 414). These materials have a large content of pozzolanic activities because of non-crystalline silica and particular surface area. It is often utilized in the lime pazzolan mixes to replace Portland cement partly. 3.0 Calcium Silicate Hydrate 3.1 What is C – S - H? 2The Calcium silicate hydrate (C-S-H) refers to the main binding components of the Portland cement paste containing 60 – 70% of fully hydrated paste. In the Portland cement, β – C2S and C3S hydrate forming calcium hydroxide (CH) and C-S-H. The shorthand nomenclature of cement is utilized through this research paper, whereby C = CaO, S=SiO2, A = Al2O3, H = H2O. C-A-S-H and C-S-H mean a variable constituent of the main species. C-S-H is almost an amorphous, contains a variety of stoichiometry (Tseng 102). Additionally, the material is capable of incorporating the guest ions, especially aluminum. Mostly, the natural component of calcium silicate hydrate tobermorite has been utilized largely for modeling the molecular structure of the C-S-H. Most probably, aluminum incorporation into the structure of C-S-H plays a vital role in the mechanical and chemical behavior of the C-S-H (Tseng 49). The Supplementary Cementitious Materials (SCMs) may be added to the concrete mixtures as a way of increasing the quality of the cement properties. The commonly used SCMs, slag and fly ash is made up substantial quantities of the reactive aluminum. Notably, it is possible to incorporate aluminum into natural calcium silicate hydrate tobermorite. C-A-S-H is a form of C-S-H that has been substituted by aluminum and it is formed after dehydrating the presence of the Al3+ ions from Portland cement. Al3+ ions become present in the component when slag and fly ash is dissolved in the water (Scheirs, John, and Long 209). Therefore, the quality of C-A-S-H is achieved in the concrete when SCMs which contains reactive aluminum components to the concrete mixtures. 3.2 What are different C-S-H phases? According to (Finch, Robert and Bullen 178), there are two types of the C – S – H phases. C – S – H is described as the basic hydration product exhibited in the form of a corrugated platelet. The two types of C – S – H are type I and II. In type C-S-H (I) the ratio of Calcium – Silicate is about 0.8 – 1.5 while for type C-S-H (II), the ratio is 1.0 – 2.0. Based on these two phases, the crystal nature of the phases increases with the Calcium – Silicate ratio. The C – S – H (I) is exhibited in the electron micrographs in the form of flakes. On the other hand, the C – S – H (II) is exhibited in the forms fiber. These fibers correspond to a rolled platelets having the CH layers as shown in the following figure; Figure 1: The Rolled C – S – H (II) Platelets Source: Nano and microstructure of Portland Cement Paste A & B – the C – S – H layers C – The interlayer region D – The spaces between rolled leaves E – The internal spaces in the roll There are five varieties of the C – S – H phases that grow during the hydration process. They are described as needle-like, gel-like, sword-shaped and flake-shaped phases. In this regard, therefore, it can be noted that the C – S – H phases can undergo different morphological changes when C3S is hydrated. 3.3 How to Investigate Different C-S-H Phases? Different C – S – H phases can be investigated using classical X – ray on concrete and mortar material in a laboratory setting. In this way, the investigator can examine the distribution and quantify the phases that occur in the structure. This new technique is capable of enabling the evaluation of the microstructure of the cementitious system through a 3 – dimensional imaging (Davidovits 129). To begin, one will select two different forms of mortar bars that are fabricated in accordance with the DIN. The first mortar can be fabricated from the mixtures of norm sand and cement in a ratio of 1: 3 while the second bar which contains 75% sand composition the remaining 25% partially replaced by the waste of glass powder (Malhotra 118). It is expected that when cement is replaced by the reactive wastes of glass powder it results in porosity reduction especially ...
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