Concrete Mix Method and Used of Pulverised Fly Ash - Lab Report Example

STUDENT’S NAME: GROUP NAME: DATE OF CASTING & TESTING LABS: NAME OF THE INSTITUTION: CONCRETE MIX METHOD AND USED OF PULVERISED FLY ASH SUMMARY The general concept is that the variation in normal strength should follow a normal distribution such that all the tests results carried out while preparation the cement content are clearly represented in the process Table of Contents Table of Contents 2 1.0 INTRODUCTION 3 1.1 CONCRETE MIX 3 1.2 PULVERISED FLY ASH 4 2.0 EXPERIMENTAL METHOD 4 2.1 The Design and Batch of a Normal Concrete Trial Mix using the BRE method 4 Table 1 5 Table 2 5 Table 3 5 2.2 Pulverized Fly Ash (PFA) as a Partial Cement Replacement 6 3.0 RESULTS 6 3.1 The significance of Fly Ash with Cement in Concrete 6 4.0 DISCUSSION 7 4.1 The Performed Standard Workability Tests 7 4.2 The Mechical properties of Hardened Cement 8 5.0 CONCLUSION 8 1.0 INTRODUCTION 1.1 CONCRETE MIX For every construction project being undertaken to be successful, the right concrete mix ratio plays a major role since it can either solve the problem or create more problems to the contractor. An appropriate concrete mix should be one that is easier to place in beneath the construction blocks, one that is expected to be durable for the life of the floor or the wall being constructed, one that is believed to be of adequate strength as per the needs of the application being initiated as well as one that is anticipated to be attractive upon the completion of the construction project (Teychenné, Franklin & Erntroy, 2007, pp.18.32). Ideally, According to Teychenné, Franklin & Erntroy (2007, pp.18.32), contractor should always seize from relying on the indication of the cement bags which despite showing the quantity of cement in the bags, it fails to acknowledge important aspects such as the stampability, pumpability, permeability, stainability, shrinkage as well as the workability of the cement which are very important areas of interests in any given project roll out. In order to ensure that the concrete mix is the right one for the application in question, the contractor should desire to have comprehensive answers for the following questions:- What is the best size of the aggregate in the project? What slump is ideal in this particular case? How will the strength of the wall or the floor under construction be achieved in the end run? Is the entrained air necessary to be taken into consideration? What will be appropriate steps to be considered in the event that the day turns out to be cold or hot? Is the fly ash necessary in this concrete mi process? Therefore, contractors should always know that a good concrete mix will always prove to be vital for the well being of their construction works. They should try and ensure that their decorative concretes are the good ones since the decorative concretes are in most cases expected to be of high strength with low permeability as well as low shrinkage (Su and Chain, 2001, pp.1800-1803). 1.2 PULVERISED FLY ASH The Pulverized Fly Ash (PFA) is among the residues produced during coal combustion and is normally consists of fine particles that are emitted from the boiler with the flue gases. During the combustion, ashes that falls at the bottom of the boiler are often referred to as bottom ash while the ashes captured by the electrostatic precipitators are known as fly ash. These ashes are thereafter used in place of Portland cement in a concrete, they tend to replace close to 30% by mass of Portland cement. However, in some cases, they can be utilized in higher quantity to replace the Portland cement since they are believe to boost the strength and increase the chemical resistance as well as the durability of the wall or the floor under construction (Ate, 2002 ,pp.752-755). 2.0 EXPERIMENTAL METHOD 2.1 The Design and Batch of a Normal Concrete Trial Mix using the BRE method According to Building Research Establishment (BRE) Ltd, designing a normal concrete trial mix involves a number of factors which are ideally categorized into two areas as followings:- Specific Variables which are values nominated based on certain parameters depending on the concrete mix required for that specific construction project. In our case for instance, we had air and water quantified as indicated below:- AIR WATER + Cube 1 2303.9 1291.2 Cube 2 2298.6 1291.2 Cube 3 2304.7 1291.7 Cube 4 Cylinder 1 3638.2 2048.3 Cylinder 2 3615.2 2046.3 Cylinder 3 3688.2 2042.2 Table 1 Likewise the specific maximum loads for the three cylinders were:- Cylinder 1 Max load……….. 324.84 Cylinder 2 Max load……….. 306.11 Cylinder 1 Max load……….. 266.14 Table 2 In our experiment, the work that was involved in the load stated above is as indicated below; Cube 1 …….. 36432 ≈ 36N/m 3 Cube 2 …….. 37422 ≈ 37N/m 3 Cube 3 …….. 32458 ≈ 32N/m 3 Table 3 In addition to the specific variables, there is some other information that is always in possession of the producer of the concrete. They may include the formulae for arriving at the velocity given the distance covered and the time taken in the process, therefore calculate the DEM, which is basically the velocity density at a given cube (Kou and Chan, 2007, pp.56-71). Once, the information above has been accurately noted down, they are evaluated and sub divided further into two categories:- The mix parameter some of which are involved in the formation of an intermediate stage towards which the subsequent category will be arrived at in the mix design process Thereafter, the final unit proportion will be determined and estimated in terms of mass of materials required to generate cubic metres of strong concrete. In the entire process of determining the normal cement trial mix, five steps have to be undertaken which includes:- STEP 1: The strengthening process so as to estimate the free water and cement ratio to be considered in the concrete preparation STEP2: The workability concept to determine the level of free water required in the process STEP 3: Merging of the step 1 and 2 to generate the cement content to be used in the preparation STEP 4: It involves estimation of the total content of the aggregate required in the process STEP 5: This involves establishment of the fine & course contents of the aggregate determined in step 4 2.2 Pulverized Fly Ash (PFA) as a Partial Cement Replacement According to Kou and Chan (2007, pp.56-71), most countries depend on coal as a source of fuel for generating power. Therefore, a number of coals based thermal power station produces a number of ashes among them, the fly ash. Fly ash is the ash emitted from the flue gases via electrostatic precipitator in a dry form and tends to have fine texture. 3.0 RESULTS 3.1 The significance of Fly Ash with Cement in Concrete In most occasions, Self Compacting Cement (SCC) is as a result of the following four mineralogical phases:- Phase 1: Tricalcium Silicate- C3S (3CaO.SiO2) Phase 2: Dicalcium Silicate-C2S (2CaO.SiO2) Phase 3: Tricalcium Aluminate-C3A (3CaO.Al2O3) Phase 4: Tetracalcium alumino-ferrite- C4AF (4CaO.Al2O3.Fe2O3) The mineralogical phases stated above normally reacts with water and as a result generate the SCC. Meanwhile, during the reaction process known as the hydration of cement, surplus substance called lime often remains in the hydrated cement. This substance tend to have deleterious effect to the concrete in that, it makes the concrete to be porous, that is, causing mini cracks while weakening the bond with the aggregate hence affecting the durability of the concrete (Browne, 2009, pp.67-69) However, addition of fly ash in the mix causes the lime to become source of pozzolanic reaction resulting to the formation of extra C-S-H gel which have the same binding properties in the concrete as those generated during the hydration of the cement concrete. During the entire process, heat is normally released which increases the temperature of the mass, likewise presence of fly ash will be responsible for strength development of the concrete mass through its reaction with the lime. The other underactive portion of the fly ash will act as micro aggregate to initiate the packing effect while increasing the strength (Browne, 2009, pp.67-69). 4.0 DISCUSSION 4.1 The Performed Standard Workability Tests Then Fly Ash elements are often spherical in shape and reduce the amount of water required for any given slump. These Fly ash as particles are also responsible for the reduction of the friction between the aggregates as well as between the concrete and the pipe line hence improving the pumpability of the cement concrete and enhancing the workability(Browne, 2009, pp.67-69). These Fly Ash particles also improve the fines volume while lowering the water content hence reducing the chances of the cement concrete bleeding. 4.2 The Mechical properties of Hardened Cement When the concrete is hardened, some of the entrapped water in the concrete mass is utilized by the cement mineralogy for hydration while some water evaporates hence leaving the porous channel to the level of volume occupied by the water. Therefore, the higher the water cement ratio, the higher will be the porosity hence higher permeability. The permeability in the process results to the ingression of the moisture as it makes the air easy thus causing the corrosion of the reinforcement 5.0 CONCLUSION Among the benefits associated with PFA includes:- Improved resistance to sulphate attack Increased long term performance in terms of strength Minimization of the hydration heat Therefore, contractors are advised to take full advantage of the gain in strength of PFA concrete beyond 28 days especially when loading additional conditions permit. BIOBLIOGRAPHY Teychenné, D.C., Franklin, R.E., Erntroy, H.C., Nicholls, J.C., Hobbs, D.W. and MARSH, D., 2007 Design of normal concrete mixes, pp. 18-33 Su, N., Hsu, K.C. and Chai, H.W., 2001. A simple mix design method for self-compacting concrete. Cement and concrete research, 31(12), pp.1799-1807. Browne, R.D., 2009. Mechanisms of corrosion of steel in concrete in relation to design, inspection, and repair of offshore and coastal structures. ACI Special Publication, pp. 65-71. Atiş, C.D., 2002. Heat evolution of high-volume fly ash concrete. Cement and Concrete Research, 32(5), pp.751-756. Kou, S.C., Poon, C.S. and Chan, D., 2007. Influence of fly ash as cement replacement on the properties of recycled aggregate concrete. Journal of Materials in Civil Engineering, pp. 47-81 Khan, M.I. and Lynsdale, C.J., 2002. Strength, permeability, and carbonation of high-performance concrete. Cement and Concrete Research, 32(1), pp.123-131. Read More