1 MIX DESIGN OF POLYMERIC CONCRETE INCORPORATING FLY ASH, RICEHUSK ASH AND SILICA FUME M.F. Nuruddin 1* , S. Qazi 2 , N.Shafiq 1 , A. Kusbiantoro 2 1 Associate Professor, 2 Research Student Department of Civil Engineering, Universiti Teknologi PETRONAS 31750 Tronoh, Perak , Malaysia. Tel 605-3687282, Fax: 605-3656716, * Email: [email protected]
ABSTRACT: The increase production of Portland cement causes great concern on theenvironment because of high carbon footprint. Besides CO 2 emission, quarrying of raw materials(limestone and clay) for the production of cement is becoming the source of environmentaldegradation. On the other hand waste disposal is also becoming a global issue because of scarcityand expensiveness of land-fills. This research study focuses on complete elimination of Portlandcement for production of concrete that can achieve 56 days cube strength in the range of 40-50MPa with the emphasis on the curing techniques applicable for in-situ construction; namely hotgunny sac, ambient and sunlight curing. This research study incorporates fly ash as a base sourcematerial and rice husk ash or silica fume as replacements of fly ash by 3%, 5% and 7%. Sodiumhydroxide and sodium silicate solution used as activators of silica (Si) and aluminum (Al) in sourcematerial and sugar based material is incorporated in the mix to increase the setting time of concrete.Compressive strength test is conducted on the specimens and it shows that at 3, 7, 28 and 56days the fly ash, rice husk ash and silica fume can be good replacements of cement. Compressivestrength of sunlight curing for the polymeric concrete reaches up to 50.96 MPa at 56 days. Keywords: Polymeric concrete, CO 2 emission, fly ash, silica fume, rice husk ash, sugar 1. INTRODUCTION Concrete has the largest production of all man-made materials with an annual globalproduction of about one cubic meter for every person on Earth as suggested byNational Research Council Canada. So globally; the consumption of concrete wasestimated to be 8.8 billion tons per year (Mehta 2001). Its sophistication lies in the factthat its constituents are universally available. Due to this fact, it has become adistinctive construction material in the world. Concrete is basically a compositemixture containing cement paste and aggregates as its main components. Cement(OPC) is manufactured using limestone, clay and other mineral, mixed in definiteproportions to produce chemical reaction during a burning process at very hightemperature. Cement results from calcination of limestone (CaCO 3 ) and silico-aluminous materials as in Equation 1 (Divya Khale, 2007).5CaCO 3 + 2SiO 2 (3CaO, SiO 2 ) (2CaO, SiO 2 ) + 5CO 2 The contribution of cement industry to the CO 2 emissions is about 5 % of theglobal CO 2 emissions (Ernest Worell, 2001) and one ton of CO 2 is released in theatmosphere from one ton production of Portland cement (J.Davidovits, 2008). CO 2 emission from a cement plant is divided into two source catagories: combustion and (1) 2 calcination. The cement sustainability initiative progress report shows thatCombustion acquires 40% whilst calcinations acquires 60% of the total CO 2 emissionsfrom cement manufacturing process. The emissions from combustion are related tofuel use and the emissions due to calcination are formed when the raw materials(limestone and clay) are heated to over 1500°C and CO 2 is liberated from thedecomposed limestone.Quarrying of raw materials (limestone and clay) for the production of cement isbecoming the source of environmental degradation. To produce one ton of Portlandcement, 1.6 tons of raw materials are needed and the extraction of raw materials fromthe earth is 20% faster than the earth replenish it, so raw materials consumed in 12months will take 14.4 months to be filled back (T.R Naik, 2000).Many researchers from the world are working on this serious issue created bycement and the solution is the introduction of polymeric cement by the development of inorganic alumina-silicate polymer (J.Davidovits, 2008). A binder can be obtained bythe reaction of industrial by-products such as fly-ash (Rangan, 2008.), (Palomo, 1999,2004), silica fume (Rao,1998) or other mining material and agricultural waste productssuch as rice husk (Deepa, 2006) with the alkaline liquid.In 1979, Joseph Davidovits created and applied the term geopolymer becausepolymerization process takes place, in which Si and Al present in the source material(FlyAsh/RiceHuskAsh/SilicaFume), reacts with the alkaline liquid to produce binders.In geopolymer, polymerization is a condensation polymerization in which water isreleased during chemical reaction and nature of reaction is endothermic. Ingeopolymerization, the polycondensation of alumino-silicate oxides (Si 2 O 5 , Al 2 O 2 ) withalkali polysilicates (Sodium or Potassium silicate) takes place producing Si – O – Albonds (Hardjito.D and B. V. Rangan, 2005).The chemical reaction may comprise the following steps (Xu and Van Deventer 2000a): Dissolution of Si and Al atoms from the source material through the action of hydroxide ions. Transportation or orientation or condensation of precursor ions into monomers. Setting or polycondensation/polymerisation of monomers into polymericstructures.Hardening of concrete much more depends upon curing temperature (Brooks JJ,2002) and curing age. For fly ash concrete, setting time was decreased by a factor of six when temperature was increased from 6 °C to 80°C (Brooks JJ, 2002) therefore 3 increased temperature gives rise to pozzolanic reaction (Kejin Wang, 2004). Atambient temperature; the reaction of fly ash is very slow (Puertas, 2000) and delay thebeginning of setting (Kirschner, 2004).Work has also been done on the development of mixture proportions (Harjito,2004) for long term and short term properties of low calcium fly ash based geopolymer concrete (Wallah, 2006). Fly ash, also known as pulverized fuel ash, is basically anon-combustible mineral portion of the coal that has been thermally altered as itcycles through the combustion process.Properties and characteristics of geopolymer concrete studied by researchers(Raoul, 2003), (Deepa, 2006) showed that RHA can be used as a binder in concrete. Rice milling produces a byproduct known as ‘Husk’ that is 20% o f rice paddy. InMalaysia, Almost 2.2 million tons of husk is produced per year from agricultureactivity, contributing to 600 million tons of annual world husks production (InternationalRice research institute). When this husk is burnt in the microwave incinerator,microwave incinerated rice husk ash (MIRHA) is generated. Recent research showsthat pozzolanic activity varies with different burning method used. Based on theresearch, RHA produced by microwave incinerator burning has the highest value of pozzolanicity (Kusbiantoro 2007). MIRHA is a fibrous material containing more than90% silica.Silica fume can also be used as a binder in concrete. It is a byproduct of thereduction of high-purity quartz with coal in electric furnaces in the production of siliconand ferrosilicon alloys and is also known as microsilica.Polymeric cements can reduce 80% to 90% of CO 2 emission as compared toordinary Portland cement (J.Davidovits, 1998) that will ultimately lead to the decreasein global warming and depletion of ozone layer. 2. METHODOLOGY2.1 Materials Selection Materials used in this study were chosen according to the specification that meets therequirement of appropriate British Standards as well as the objective of this research.Fly ash was obtained from Manjung power station, Lumut, Perak. Chemicalcomposition of fly ash is shown in Table 1 (Chin 2007). 4 Table 1. Chemical Composition of Fly ash (Chin, 2007) Compounds Percentages (%)SiO 2 51.19 Al 2 O 3 24Fe 2 O 3 6.6CaO 5.57MgO 2.4%SO 3 0.88K 2 O 1.14Na 2 O 2.12 Rice husk utilized in this research was taken from rice milling plant Bernas,Malaysia (Kusbiantoro 2007). Rice husk was dried in direct sunlight to decrease itsmoisture so as to produce less amount of smoke during burning process. Chemicalcomposition of MIRHA is given in Table 2. Table 2. Chemical Composition of RHA (Chin, 2007) Compounds Percentages (%)SiO 2 86.1 Al 2 O 3 0.17Fe 2 O 3 2.87CaO 1.03MgO 0.84SO 3 0.41K 2 O 4.65Na 2 O - Coarse aggregate used in this experiment is crushed and maximum size of 20 mm(BS 812-103.2 1989) while the fine aggregate used is natural Malaysian sand with thefineness modulous of 2.7, classified in zone 3. Fine aggregate was also sieved for thesize less than 5mm. 5 Sodium silicate (Grade A53) used in a solution form mixed with 56.31% of water,29.43% of SiO 2 and 14.26% of Na 2 O. Sodium hydroxide used was in the form of pellets. Concentration of solution was 8M and in order to make 1 Kg of solution,29.4% of pellets were added to the water.Sugar was used to increase the setting time of concrete. Adding plain white sugar in concrete prevents the cement from joining with the water and slows the hardeningof the minerals (Keelin McDonell, 2006).Water used in the mix was tap water that was free from all types of harmfulchemicals, organic material, oil, chloride, silt and suspensions (B.S. 3148:1980). 2.2 Design of mix compositions Class F fly ash was used in the research as a base binder for all mixes. Density of flyash for control mix was 350 kg/m 3 and was replaced by 3%, 5% and 7% by MIRHA or silica fume. All other material quantities were kept constant in order to see the effect of replacement of MIRHA or silica fume on the properties of concrete.Sodium silicate to sodium hydroxide ratio was 2.5 & coarse to fine aggregate ratiowas approximately 1.86. Sugar based material is used as 3% of the total binder. Extrawater (other than the water present in solutions) has been added to the mixture equalto 10% of the total binder to ensure workability.Symbols A, B and C show samples cured with hot gunny, ambient temperatureand sunlight respectively and 1, 2, 3 and 4 show percentage replacement of MIRHA or silica fume by 0%, 3%, 5% and 7%. They are shown in Table 3. 2.3 Casting and Curing Cubes of dimension 100 mm were cast and after 24 h of casting; moulds wereopened. Three types of curing methods have been adopted namely hot gunny curing,ambient curing and sunlight curing.For the hot gunny curing samples were covered with gunny sack; dipped in warmwater that was renewed the next day and removed from the samples the third day.For ambient curing, samples were placed in the shade outside the lab and insunlight curing samples were put in a plastic coated shelve; exposed to direct sunlight.