-
The Effect Of Water/cement Ratio On Compressive Strength Of Palm Kernel Shell Concrete At 1:2:4 Nominal Mix
CHAPTER TWO -- [Total Page(s) 4]
Page 2 of 4
-
-
-
The water to cement ratio, or w/c ratio, largely determines the strength and durability of the concrete when it is cured properly. The w/c ratio refers to the ratio of the weights of water and cement used in the concrete mix. A w/c ratio of 0.4 means that for every 100 lbs of cement used in the concrete, 40 lbs of water is added.
For ordinary concrete (sidewalks and driveways), a w/c ratio of 0.6 to 0.7 is considered normal. A lower w/c ratio of 0.4 is generally specified if a higher quality concrete is desired. The practical range of the w/c ratio is from about 0.3 to over 0.8. A ratio of 0.3 is very stiff (unless super plasticizers are used), and a ratio of 0.8 makes a wet and fairly weak concrete. For reference, a 0.4 w/c ratio is generally expected to make a concrete with a compressive strength (its f’c) of about 5600 psi when it is properly cured. On the other hand, a ratio of 0.8 will make a weak concrete of only about 2000 psi.
The simplest way to think about the w/c ratio is to think that the greater the amount of water in a concrete mix, the more dilute the cement paste will be. This not only affects the compressive strength, it also affects the tensile and flexural strengths, the porosity, the shrinkage and the color.
The more the w/c ratio is increased (that is, the more water that is added for a fixed amount of cement), the more the strength of the resulting concrete is reduced. This is mostly because adding more water creates a diluted paste that is weaker and more susceptible to cracking and shrinkage. Shrinkage leads to micro-cracks, which are zones of weakness. Once the fresh concrete is placed, excess water is squeezed out of the paste by the weight of the aggregate and the cement paste itself. When there is a large excess of water, that water bleeds out onto the surface. The micro channels and passages that were created inside the concrete to allow that water to flow become weak zones and micro-cracks.
Using a low w/c ratio is the usual way to achieve a high strength and high quality concrete, but it does not guarantee that the resulting concrete is always appropriate for countertops. Unless the aggregate gradation and proportion are balanced with the correct amount of cement paste, excessive shrinkage, cracking and curling can result. Good concrete results from good mix design, and a low w/c ratio is just one part of a good mix design.
2.3 DESCRIPTION OF PALM KERNEL SHELL (PKS)
Palm kernel shells are known to have hard and stony endocarps that surround the kernel and the shells are usually in different shapes and sizes. They are light and are naturally sized; they are appropriate for replacing aggregates in lightweight construction, since they are known to be hard and of organic origin, once used to produce concrete matrix, CEB-FIP, (1977). This gives lightweight concrete made with palm oil shell an advantage over aerated concrete, since permeability is low and the chance for carbonation is reduced.
Okafor, (1988), described palm kernel shell to have irregular shape after cracking and therefore its shape cannot be defined. The shape takes pattern of cracking on the shell and usually composed of many shapes ranging from parabolic or semi-circular shapes, flaky shapes and other irregular shapes. After cracking the edges of the shells are rough and spiky and the overall shapes become concave and convex with a fairly smooth surface. There is no fixed thickness for the shell, this depend on the species from which it is obtained, ranging from 1.5 mm to 4 mm and usually between 2mm and 3mm.
CHAPTER TWO -- [Total Page(s) 4]
Page 2 of 4
-
-
ABSRACT - [ Total Page(s): 1 ]ABSTRACT IS COMING SOON ... Continue reading---
APPENDIX A - [ Total Page(s): 2 ] ... Continue reading---
CHAPTER ONE - [ Total Page(s): 3 ]CHAPTER ONE1.0 INTRODUCTION Concrete is a composite engineering material made from the mixtures of cement, water, fine aggregate (sand), coarse aggregates (such as crushed stones or rocks and granite) and a small amount of air in a specific proportion that hardens to a strong bony substance or become ossified. The cement always serves as a binder for the aggregate.The uniqueness quality of concrete makes it desirable as a building material, because it can be moulded into virtually ... Continue reading---
CHAPTER THREE - [ Total Page(s): 3 ]CHAPTER THREE3.0 METHODOLOGYFor better achievement of this project, the following stages are ensured:ï¶ COLLECTION OF MATERIALS The materials comprises of cement, sand, palm kernel shell and water. Palm kernel shell was obtained from a local palm kernel producing village Oko, Irepodun LGA, Kwara State Nigeria.ï¶ PREPARATION OF PALM KERNEL SHELL (PKS)Due to high water absorption of palm kernel shells, it is mandatory to soak the aggregate for about 30 minutes. It i ... Continue reading---
CHAPTER FOUR - [ Total Page(s): 6 ]CHAPTER FOUR4.0 DISCUSSION OF RESULTS4.1 Properties of Palm Kernel Shell {PKS}Results of the study from table 4.1 and figure 4.1 shows that the sieve analysis of PKS and the trend of the percentage cumulative weight retained increases as the sieve sizes decrease. The specific gravity of PKS was found to be 1.37 [Table 4.2] which [Okpala; 1990] classified as light weight aggregate.The water absorption capacity was found to be 10% [Table 4.3]. This value was considered in the design of m ... Continue reading---
CHAPTER FIVE - [ Total Page(s): 1 ]CHAPTER FIVE5.0 CONCLUSION AND RECOMMENDATION5.1 CONCLUSIONi. The result of the physical properties obtained show that PKS can be used as partial or complete aggregate substitution for lightweight structural concrete at 1:2:4 nominal mix.ii. The compression strength increases with advancement of age but decreases with increase in water cement ratios. That is, at w/c ratio of 0.3 the compressive strength is 6.5N/mm2 at 28 days while at w/c ratio of 0.5, it is 3.99N/mm2 at ... Continue reading---
REFRENCES - [ Total Page(s): 1 ]REFERENCENeville, A.M. (1996). “Properties of Concreteâ€. Longman Group Limited, London.Okafor, F.O. (1988). “Palm Kernel Shell as Aggregate for Concreteâ€. Cement Concrete Research Vol. 18, No 6, pp. 901-910.Okpala, D.C. (1990). “Palm Kernel Shell as a Lightweight Aggregate in concreteâ€. Building and Environment 25, pp. 291-296Olanipekun, E.A., Oluola, K.O., and Ata, O. (2006). “A comparative Study of Concrete Properties Using Coconut Shell and Palm Ker ... Continue reading---
