Conventional concrete is porous and the network of pores allow the passage of harmful substances through the concrete internal structure thereby causing damage to the internal structure of the concrete and which resulted in consequential loss of concrete durability. Efforts have been made to protect concrete but problem still exist such as in adequate protection and high cost of protection in view of the drawbacks this research work investigates effects of permeability reducing admixture on thedurability properties of binary cementitious matrix concrete.A total of 342 sample specimens of 100mmx100mmx100mm cubes were cast with the following connotations, 100% cement, 2% PRA, 10% C S A, 15% C S A, 2% PRA + 10% C S A and 2% PRA + 15% C S A, The permeability reducing admixture was purchased from Market, The coconut shell was pre ashed in an open air for one hour and was allowed to cool then calcined at temperature of 8000C in a kiln for 4hours and was allowed to cool to room temperature before it‟s removal from the kiln, the Coconut Shell ash was used to replace cement at 10% and 15% replacement. 90 specimens were tested for compressive strength, 90 specimens were tested for compressive strength in aggressive environment (MgSO4), 162 specimens were tested for water absorption capacity, sorptivity and abrasion resistance. The plain concrete, the plain concrete modified with PRA, Blended concrete and Blended concrete modified with PRA were cured in water and their respective properties were evaluated at 14, 28, 56, 90 and 180 days curing period respectively. The control sample had the highest compressive strength test of 33.85N/mm2 at 28 days, however at 56 days all the samples exceeded the control in strength except 15% CSA that had 32.95 N/mm2, at 90 and 180 days all the samples exceeded the control, Ninety samples were immersed in aggressive media i.e exposure to 2.5% magnesium sulphate solution, compressive strength was used to determine the severity of the effects of MgSO4on concrete samples, at 90 days all the samples loss strength but the loss was more severe in control sample, the control loss 17.7% of its strength, 2% PRA loss 1.6% , 10% CSA loss 3.8% at 90 days, 15% CSA loss 4.75% at 90 days, 2% PRA+ 10% CSA loss 1.0% and 1.3% of its strength at 90 days, 2% PRA+ 15% CSA loss 0.76% at 90 days, at 180 days it was discovered the effect was more severe on control samples and less severe on all other samples, absorption capacity test revealed that the PRA modified Pozzolana blended cement concrete had the lowest water absorption of 0.87% at 90 days, the PRA modified Pozzolana blended cement concrete had the lowest sorptivity of 0.62 at 90 days. Based on the above findings it was concluded thatPRA modified pozzolana blended cement concrete is most durable, then it was recommended that it could be used for concrete production in soil that its Magnessiumsulphate content is high and where concrete may be subjected to water ingression.
1.1 Background of the Study
Waste is one of the major threat facing present generation (Safiuddin, Zamin, Salam, Islam, and Hashim, 2010). Large quantities of waste materials and by-products are generated from manufacturing processes, agricultural activities, service industries, construction activities and municipal solid wastes, solid waste management has become one of the major environmental concerns in the world, with the increasing awareness about the environment, scarcity of landfill space and due to its ever increasing cost, and strict environmental control laws in some countries there hasbeen a growing emphasis on the utilisation of waste materials and by-products as construction materials, especially concrete (Patricija, Aleksandra, Korjakson, and Stokeman, 2012).
According to Dahiru(2007) Construction activities consumes approximately 40% natural resources and 40% waste is generated as a result of such development, that is why two of the basic actions towards sustainability highlighted in Rio generio in Brazil agenda 21 are minimization of total waste generation and maximization of environmental sound waste management and recycling. Remedial measures were outlined to solve the problems of waste prominent among them is what is popularly called Three Rs – Reduce, Re use and Recycle (Zongji, 2011).
Recently, the interest for utilization of waste materials in cement or concrete has increased significantly (Karim, Zain, Jamil, Lai and Islam, 2012). In advanced countries, partial replacement of cement with pozzolanic industrial wastes is well documented and recommended(Manaseh, 2010). In the developing countries, the most common and readily available materials that are used to partially replace cement without economic implications are agro based wastes, with inherent multiple benefits (Manaseh, 2010). One of the locally available agricultural wastes that satisfies the requirement of sustainable development and, which can be used as partial replacement of Ordinary Portland Cement is Coconut Shell Ash (CSA).Coconut Shell ash essentially contains amorphous silica 37.97%, Al2O3 24.12%, Fe2O3 15.48%, Cao 4.98%(Vignesh, Aruna, Manohari, and Maria, 2014). Supplementary cementitious materials reduce lime content in hydrated Portland cements and replace it with pore filling cement hydrates, which are known to improve the ultimate strength, impermeability and concrete resistance to chemical attack (Shetty, 2009).
Pozzolans are materials that consist predominantly of silica and aluminaand are able to combine with ordinary Portland cement in the presence of water to produce new reaction products exhibiting a binding character. Therefore, they are widely used as an additive in cement in which portlandite is a major hydration product. Their widespread use can be explained both by their beneficial effect on the properties of concrete as well as by the economic and ecologic advantage of their use (Martensetal., 2009).Some of the pozzolanas are natural, others are by-products (artificial) and both contains silica in amorphous form and will react with calcium hydroxide (CaOH2) to form more cementitious calcium silicate hydrate (C S H) and contribute to the concrete strength (Habeeb and Mahmud, 2010). The improvement in the properties of concrete with blended cements is attributed to the pozzolanic reactions taking place between the oxides originating from the supplement material and the hydration products of ordinary portland cement (Khan, 2010).
Blended cement is defined as Portland cement containing other finely dividedparticles in different but well-defined proportions (Salaudeen and Leeyee, 2008). Mostrecently blended cement based on industrial and agricultural waste, are well known fortheir improved long-term strength and durability. The blending agents are such as fly ash (FA), ground granulated blast furnace Slag (Slags), rice husk ash (RHA), palm oil fuelash (POFA), SF (SF), coconut shell ash (CSA) calcined clay etc. It is reported to improve rheology andcohesiveness, lower heat of hydration, lower permeability and higher resistance to chemical attack. In some cases, a boostingearly strength becomes apparent, while in others, an increase in later strength occurs.In recent years, the applications of blended cements have been further extended(Salaudeen and Leeyee, 2008).
Many researches have been conducted on Cocoanut shell ash as partial replacement of ordinary portland cement and strength was used as its quality performance index (e.g Oyedepo,Olanitori, and Akande, 2014: Vignesh et al., 2014: Utsevu and Taku, 2012). It was reported that 10% replacement of cement with coconut shell ash gives highest strength of 20.74N/mm2, 31.78 N/mm2 , and 31.78 N/mm2 respectively, However Utsevu and Taku (2012) further recommended 15% replacement level with strength of 23.23 N/mm2. However the durability properties of cocoanut shell ash blended cement was not assessed. One of the main reason for deterioration of concrete in the past is that too much emphasis is placed on compressive strength, as a matter of fact advancement in concrete technology has been generally on the strength of concrete it is now recognized that strength of concrete is not sufficient (Shetty, 2009). The degree of aggressiveness of the environmental condition to which the concrete is exposed over it‟s entire life is equally important (Shetty, 2009). Therefore one of the essence of this research work is to assess the durability properties of concrete produced using Cocoanut Shell Ash (C S A) ash as partial replacement of ordinary Portland cement.
Permeability reducing admixture is added to the concrete mix and can be in liquid form or powdered form and are introduced into the concrete mix according to the manufacturer‟s specifications which is 2% the weight of cement (AC1 212 3R, 2010).Mukeshi, Singh and Singh (2009) carried out research on the effects of water proofing admixture on the hydration of Portland cement and concluded that properties of concrete that contains water proofing admixture (strength and durability) improve when compared with conventional concrete. However there still exist the need to investigate the effect of Permeability Reducing Admixture on properties of binary cementitious matrix concrete made with coconut shell ash as partial replacement of ordinary Portland cement.
Therefore this research work seek to assess the effects of permeability reducing admixture on the properties of binary cementitious matrix concrete produced with coconut shell ash as partial replacement of cement.
1.2 Statement of Research Problem
Concrete and other cementitious surfaces are porous, the pore size of concretes lies between (10 nano to 50 micronmeters). These pores allow water and soluble contaminants to penetrate the structure leading to degradation. The effects of degradation can include efflorescence, laitance and physical defects such as cracking and spalling (Mukeshi et al.,2009).
The crack joints and other defects in the concrete facilitate the ingress of water, which is actively transported from area of high concentration to those of low concentration within the interior space of concrete. Water seeping is a major problem in construction industries particularly when the buildings are constructed in damped environment, when concrete is under hydrostatic pressure on one surface, water passes through the channels formed by the inter connecting cracks and voids to the other sides surface (Mukeshi et al., 2009).
Water in its various forms, such as seawater, groundwater, river water, lake water, snow, ice, and vapor, is undoubtedly the most abundant fluid in nature. Water molecules are very small and, therefore, are able to penetrate into extremely fine pores or cavities. As a solvent, water is noted for its ability to dissolve more substances than any other known liquid. This property accounts for the presence of many ions and gases in some waters which, in turn, become instrumental in causing chemical decomposition of solid materials (Mehta and Monteirro, 2006).
The use of concrete has been extended to aggressive environment and this greatly resulted in defective concrete and durability failure of concrete, a tremendous effects on the economy and environment (Naik et al., 2006). In industrialized countries over 40% of the total resources of the building industry are applied to repair and maintenance of existing concrete structures and less than 60% are applied to new installations (Naik et al., 2006).
Many researches have been conducted on the possibility of improving the durability of plain concrete, one of the materials commonly used are pozzolana. In order to reduce concrete pore structure, addition of pozzolanic materials provides secondary hydration which reduces pore volume to achieve denser, stronger and durable concrete (Siyu, et al., 2013). Many researches have also been conducted on the performance of plain and blended concrete exposed to aggressive environment i.e magnesium sulphate attack, water absorption, sorptivity test etc. It was reported that blended concreteconserves higher strength than plain concrete after exposed to aggressive environment (Vedalakhshimi, Sundra, Siwasan and Gana, 2005: Ramezanni, Pourbek and Moodi, 2013). Zhang and Zhong(2014) reported that blended concrete reduces water absorption and sorptivity.
Beatrix (2010) reported that the incorporation of supplementary cementitious materials into concrete matrix as partial replacement of cement may slowdown chemical attack on concrete for sometime but may not prevent chemical attack on concrete for a long period of time. Blended cement is not good enough for protecting concrete under aggressive environment for example exposure to magnesium sulphate for a long period of time (Ahmad et al.,2008).According to Ahmad (2014) Although partial replacement of cement with pozzolans decreased the pore volume, surface scaling increases due to the increased proportion of small diameter pores and the associated growth of capillary suction and surface area for evaporation. Many additional efforts have been made in order to protect the concrete against the influence of aggressive environment example of such is surface coating of concrete, surface coating of concrete provides adequate protection. However problems still exist these include, adequate curing of the concrete before coating is applied in order to eliminate the separation of the surface treatment, the application of surface coating requires training of the operatives and potential of decohesion when exposed to weather elements. Using a water-based solid acrylic polymer resin did not provide adequate protection of concrete against physical sulphate attack (Ahmad, 2014).
However this research seek to investigate if addition of permeability reducing admixture to a binary cementitious matrix concrete will improve the performance of binary cementitious matrix concrete when it is exposed to aggressive environment.
1.3 Significance of the Study
The recycling process appears to be a good way of conserving natural resources (limestone) and eliminates the need for waste disposal and its harmful effects by recycling available waste materials (Safiudeen et al.,2010: Obilade, 2013: Akinkunrolero, Aribisala, Oke and Ogundipe, 2013). Utilization of waste materials and by products in concrete will present partial solution to environmental and ecological problems (Sarath, Vamsi and Saha, 2012).
Permeability reducing admixture will provide efficient and effective protection to concrete by blocking concrete pores through creation of crystals in the presence of water, prevents water percolation in concrete and becomes a permanent part of concrete therefore protecting the concrete and enhancing it‟s performance during service life (Mukeshi et al.,2009). Permeability reducing admixture provides cost effective means of concrete protection when compared with membrane coatings because membrane coating requires training of the operatives, purchase of spraying devices and prone to decohesion when exposed to weather elements (Yuers, 2013). Sussane (2013) Adding Permeability reducing admixture treatment to the concrete mix at the batch plant ensures that the crystalline formation occurs uniformly throughout the structure, rather than penetrating from the surface, as would be the case with a surface application.
There is need to conduct more research on the compatibility of permeability reducing admixture with binary cementitious matrix concrete derived from agro waste (Rice Husk Ash, Coconut Shell Ash etc) and industrial by products (Fly ash, Ground granulated blast furnace slag) and potential benefits that such combinations will yield for concrete.
When both chemical and mineral admixtures are added during hydration of cement, the process of hydration become more complex but at the same time the properties of cement especially strength and durability are modified considerably (Mukeshi et al.,2009). Improved durability of infrastructure materials has ecological benefits, a durable concrete has far reaching positive influences on sustainable development in the construction industry (Naik et al., 2006).
Therefore adding permeability reducing admixture to binary cementitious matrix concrete that contains coconut shell ash as partial replacement of cement will improve concrete durability through complex hydration chemical reaction that took place between the cement paste and pozzolana and the crystal develop by the PRA. The pozzolana will react with Ca(OH)2 and produce secondary hydration process CSH there by refining the concrete pore structures, and the crystals produced by the PRA will also block the concrete pores, heal autogenous crack and there producing synergistic effects of delay hydration process, delay strength and thereby result in improve strength at later age and improve pore structure thereby improving durability of concrete (resistance to chemical attack, water absorption and fluid transport through concrete)
1.4 Aim and Objectives
The aim of this study is to evaluatethe effects of permeability reducing admixture on properties of binary cementitious matrix concrete with a view to establishing it‟s suitability for concrete production.
To determine physical and chemical properties of Cocoanut shell ashTo determine the properties of fresh concrete samplesTo assess the durability properties of concrete samplesTo evaluate thecompressive strength of concrete samples
1.5 Scope and Limitations
This study concentrated on evaluation of workability of fresh concrete (Using slump and compacting factor test), compressive strength, abrasion resistance and water absorption and sorptivity of various specimen samples, strength retained after exposure to aggressive environment.
The non-availability of standard apparatus for conducting permeability test limited this research work. Indirect methods of measuring permeability test were adopted which are Sorptivity and water absorption, These tests were conducted in place of permeability test. The results of sorptivity and water absorption tests were presented and explained. Since permeability test was assessed indirectly in the research work, the potential of utilization of permeability reducing admixture was partially assessed.
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