ABSTRACT
Polymer concretes (PCs) are known to be less permeable to water, but its usage is less popular in tropical countries like Nigeria because its common binder, thermoset resins, are very sensitive to rising temperature. This sensitivity to temperature accelerates the polymerization process and this jeopardizes its early strength development, thereby producing a PC with low workability and high porosity. To address this, polymer inhibitors with addition of Methyl Methacrylate (MMA) was introduced. Firstly characterization work on binder formulation was carried out by introducing Methyl Ethyl Ketone Peroxide (MEKP) and cobalt Naphthenate (CoNp) into the polyester resin as accelerators. Properties like density, specific gravity, particle size distribution, surface area, morphology and chemical composition were carried out on fillers. Sorghum Husk Ash (SHA) and calcium carbonate (CaCO3) were added as fillers. PC with optimum mix proportion at low binder (11%) and different filler contents (12, 14/ & 16%) were investigated under compressive test. Two types of PC (PC-SHA and PC- CaCO3) with polyester binder were produced and its physical and mechanical properties were tested. PC-SHA gave highest compressive strength (56.6N/mn2) at 14% filler contents and least water absorption of 0.26% at 16% filler contents after 28 days as compared to compressive strength value of PC-CaCO3 (49.8N/mm2) and water absorption of 3.1% at 16% filler contents after 28 days. Conclusively, SHA is seen to be highly promising filler for PC after being modified by grinding.
CHAPTER ONE
1.0 INTRODUCTION
1.1 Background to the Study
Generally, concrete-polymer composite is a concrete that contains polymers. Development of concrete-polymer composites such as polymer-modified concrete, polymer concrete and polymer-impregnated concrete aim to produce high-performing and versatile construction materials.
Polymer-modified concretes are composite materials comprising two solid phases – the aggregates that are intermittently dispersed via the materials and the binders in which itself contains a cementitious phase and a polymer phase (Gemert, 2007). The polymer introduced acts as polymeric admixtures/modifiers in normal concrete (Khudhair et al., 2018). There are economically available polymeric admixtures/modifiers in Japan categorized into polymer dispersions, redispersible polymer powder, water-soluble polymers, and liquid polymers (Ohama, 2007). On the other hand, the term ‗polymer-impregnated concrete‘ coined by Bhutta et al. (2013) refers to concrete produced by impregnating or infiltrating the hardened conventional concrete with a liquid monomer and afterwards completing the polymerization of the monomer in-situ. The area of application of polymer- impregnated concrete has been identified in precast products, though in less applications, majorly for enhancing the waterproofing ability and durability of concrete structure (Ohama, 2007).
The only non-cementitious concrete-polymer composite is polymer concrete. Polymer Concrete (PC) is manufactured by polymerizing dry aggregate and monomers (binder) after the addition of additive, catalyst or accelerator. The fresh
PC are then cured completely devoid of water and cement binder (Ohama, 2007). Its constituents depend on its designed application. PC has finite possible applications in the construction industry. It is useful in manufacturing box culverts, hazardous waste containers, trench lines, floor drains, and for the repair and overlaying of damaged concrete surface (bridge and pavements) (Bedi et al., 2013). However, some improvement and modification has to be made to improve the properties of PC. Due to this reason, many researchers have conducted several studies to develop materials that can be incorporated into PC, majorly by introducing fillers into the PC mixture (Barbuta et al., 2010).
In Japan, the concrete-polymer composites are applicable as sustainable construction materials and have been continually enhanced since the early 1920s (Ohama, 1997). Its application in the Japan construction industry is common, popular and dominant during the 1950s to 1970s (Ohama, 1997; Shaw, 1985). Other than Japan, the United States, United Kingdom, Russia and Germany have also published their standardization works of concrete-polymer composites with, occasionally, clear differences in the content (Khalid et al., 2015). In Nigeria, the use of concrete-polymer composites is still not popular. This also applies to research on PC because polymers are very reactive to hot temperature and Nigeria is a tropical country. Therefore, the lack of technical know-how among local fabricators and material scientists has become a limitation for the production of PC.
Polymer concrete is produced from polymer resin-which acts as the only concrete binder, dry inert granular aggregates, and filler. Since it does not contain cementitious materials and water, its hardening follows the polymerization process when additives, catalysts, or accelerators are added. PC containing fillers has better mechanical properties due to its effective dispersal in the mixture and its ability to induce dense concrete mixture packing. However, the type of filling materials (natural, granulated, or synthetic) also plays a pivotal role in affecting the composite characteristics (Ates & Barnes, 2012).
In this study, polyester resin was employed as binder. Since this polymer binder is temperature sensitive, polymer inhibitor additive was applied into the binder formulation to initiate the designed modification. It was expected that this would give rise to lower, yet, sufficient binder concentration for PC. This study utilized low cost thermosetting polyester resin as binder. Also, this study used Sorghum Husk Ash (SHA) from agricultural waste as filler and added into concrete mix with low binder concentration. SHA was selected as the filler in this research work, since it is available and a bye product of agricultural waste in Nigeria. Sorghum husk, an agricultural waste from milling of guinea corn, is mostly disposed as agricultural waste in landfills. Its reutilization has the potential to generate sustainable and productive materials.
The Performance of PC incorporated with SHA filler was evaluated from an engineering viewpoint. Presently, there are no published findings and data for such PC incorporating agricultural waste in Nigeria. This study has conducted extensive experiments to develop and encourage innovative usage of such sustainable and intelligent material in the Nigeria construction industry.
1.2 Statement of the Research Problem
Polymer Concretes are regarded as less permeable concrete with improved strength (Sung et al., 1997). Its usage is usually employed in liquid containing structures (Mani et al. 1987). In PC, thermoset polymer resin is used as the binder. Thermoset resins that are economically available include epoxy, vinyl-ester, and unsaturated polyester resin. These are typical resins employed in the construction industry because of their higher strength and stiffness which makes them better than thermoplastic polymers. However, epoxy and vinyl-ester resins are costlier than polyester resins (Yang & Lee, 2001). Hence, Khalid et al., (2015) mentioned that, most researchers frequently choose unsaturated polyester resin, despite the fact that it is very sensitive towards temperature. Generally, high temperature can speed up the polymerization process, resulting in PC which fails to achieve its early strength and causing other problems such as poor workability and honey comb. Therefore, polymer modification should be considered to solve the aforementioned problem by prolonging the working life and giving sufficient time for PC production in ambient temperature.
Agricultural waste like sorghum husk, disposed on open fields can adversely impact our environment through pollution (Elbasiouny et al., 2020). Therefore, it is necessary that a study is carried out to suggest an alternative solution to this problem. This study is therefore conducted to re-utilize sorghum husk to serve as fillers in PC. Agricultural waste ashes can become a cost-effective material since mineral-filled PCs are costlier. However, not all agricultural waste ashes have the potential to become PC filler. The wrong selection of filler material may lead to worsened PC quality, also it affects the PC‘s workability and process ability (Bignozzi et al., 2000).
On the other hand, air voids entrained or entrapped in hardened PC during the mixing and placing of fresh PC can significantly influence the permeability of the hardened PC. These air voids can be easily identified as visible pores on the hardened concrete. An increasing number of pores can reduce the strength of the PC (Rashid & Mansur, 2009), but the development of air voids can be efficiently reduced by using suitable micro-filler (Khalid et al., 2019). However, some modifications on the raw materials including the filler are essential to enhance their properties and improve their engineering behaviours.
1.3 Aim and Objectives of the Study
The aim of this research is to evaluate the influence of sorghum husk ash, an agricultural waste as micro-filler in polymer concrete with a view to reducing visible pores in hardened PC to enhance its strength and permeability.
The objectives of the study are listed as follows, to:
i. Formulate binder using polymer
ii. Characterize fillers under physical and chemical examination
iii. Determine the physical properties of PC containing SHA as micro-filler.
iv. Evaluate the compressive strength property of PC containing sorghum husk as micro filler.
1.4 Scope of Study
The scope of this study was to accomplish the objectives stated above and concentrate predominantly on experimental works. The testing method and work procedures were specified according to the Japanese international standard (JIS), Eurocode standard (BS- EN), American society for testing and materials (ASTM) and other recommended test procedures proposed by previous researchers.
All cement hydrate binders of conservative mortar or concrete were replaced in this study with polymer binders to produce PC. Hence, PC concrete are concrete without cement and water but made of resin binder only. The major component of PC used as polymer binder in this research is the thermosetting polyester resin. The chemical mixed with the resin was limited to 0. 5% Cobalt Naphthenate (CoNp) and 1% Methyl Ethyl Ketone Peroxide (MEKP) as recommended in earlier research findings in the literature (Rebeiz et al., 1992; Gorniski et al., 2004 & Gorninski et al., 2007) to fabricate the proposed binder design for this research. Though, following the work of Li and Lee (2002) varying percentages of inhibitor additive of Methyl Methacrylate (MMA) were added to the resin mix to have sufficient working time in producing the PC. To get consistent outcomes, the PC specimens were cast in room temperature with the relative humidity around 66 ± 2%. After that, all specimens were post-cured. Control specimens had been produced where no filler was incorporated.
SHA was utilized as the filler in PC and it was used to substitute Calcium Carbonate in conventional filled-PC. SHA filler was grinded and physically modified to obtain finer particles. Inert granular materials such as coarse and fine aggregates were utilized as well and this is similar to conventional concrete. After that, all specimens were post- cured in sunny environment. The characteristics of SHA and Calcium Carbonate fillers were examined to determine its performance from an engineering perspective and the assessment of PC on the engineering properties with optimum mix design and mix proportion were done because it is an important factor in developing the potentially valuable construction materials.
1.5 Justification For the Research
SHA can be found in abundance as agricultural waste that is often uncontrollably dumped in landfills and burnt in most environment causing air pollution which is hazardous to human health and affecting the ozone layer leading to global warming. Recycling SHA as a potential filler in PC helps in turning waste to wealth and contributing to a sustainable and cleaner environment. Nevertheless, not all waste ashes have the potential to become PC filler. The wrong selection of filler material may lead to worse PC quality. Not only that, it affects the PC‘s workability and process ability (Bignozzi et al., 2000). Most natural waste source from agricultural plant is cellulose (Raveendran et al., 1996; Kaddami et al., 2006) which has a structure that attracts liquid into PC. This can lead to excessive resin consumption, which is not cost effective, and thus jeopardise the production of PC even when filler is used. Until today, no study has so far been done on the incorporation of SHA as PC filler because of the aforesaid potential setbacks.
This research is to give an insight into the potential incorporation of SHA as micro-filler into PC, gauged through microstructure and strength examination.
The significant findings of this research will inspire the production of PC in regions under tropical temperature climate and promote its usage amongst Nigeria fabricators of building and civil engineering elements. A notable novelty database of concrete polymer composites and its application in the construction industry will be provided. The outcomes of this work will be beneficial to researchers and engineers working in the field of cellulose filler in PC. Fabricators and engineers will be updated in improving the quality of materials and providing an established database for design works in the future. Value- added products from local resources will be developed to promote green materials in the construction industry via this composite production. This research will facilitate the introduction of materials with proven performance to contractors and provide-significant market value where the final product can be commercialized.
This material content is developed to serve as a GUIDE for students to conduct academic research
INFLUENCE OF SORGHUM HUSK ASH AS MICRO-FILLER IN POLYMER CONCRETE
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