ABSTRACT
Clinker, gypsum and limestone were obtained from an indigenous cement manufacturing company. The clinker and gypsum were ground together to produce ordinary Portland cement (OPC) which served as reference cement. Limestone composite Portland cements containing 5, 10, 15, 20, 25 and 30 % limestone were prepared by adding limestone to the OPC. Two foreign and two local brands of cement were purchased from the local market in Gboko, Benue state. The cement samples were subjected to chemical and physical tests using standard methods of analyses. Data were analysed using SPSS version 18 to compare the experimental, market and standard (OPC) cements. Analyses of clinker showed the following % composition: Silicon dioxide (20.23), alumina (6.29), ferrite (3.30), lime (65.48), sulphite (0.79), loss on ignition (2.17), free lime (0.87). The litre weight was 1274g/L. Percentage compositions of limestone were: total carbonate (91.08), lime (51.00) and loss on ignition (40.21). Percentage compositions of gypsum were: sulphite (42.31) and purity (90.97). Analysis of OPC showed the following percentages: silicon dioxide (17.75), alumina (6.09), ferrite (3.41), lime (64.62), sulphite (2.72), loss on ignition (1.50), free lime (0.88), particle size [45 micron (21.73), 90 micron (3.33) and 180 microns (1.33)], Blaine 297m2/kg; soundness 1.67 mm; consistency 27.97, Vicat plunger penetration 5.70 mm; initial setting time 107.33 mins; final setting time 180.67 mins; 2 days strength 26.27 MPa; 7days strength 31.07 MPa and 28 days strength 36.20 MPa. Analysis of various limestone composite Portland cement (%) were: silicon dioxide (17.00-17.64), alumina (5.99-6.08), ferrite (3.12-3.37), lime (64.70-64.97), sulphite (2.27-2.68), loss on ignition (3.69-13.25), free lime (0.55-0.83), particle size [45 micron (19.87-30.33), 90 micron (2.13-5.93) and 180 microns (0.53-2.40)], Blaine (316-413) m2/kg, soundness (0.67-1.17) mm, consistency (24.80-27.60), Vicat plunger penetration (5.33-6.00) mm; initial setting time (115.33-126.00) mins, final setting time (183.00-229.33) mins, 2 days strength (17.28-25.00) MPa, 7 days strength (22.68-32.07) MPa and 28 days strength (28.47-34.77) MPa. Analysis of brands of Portland cement (%) showed: silicon dioxide (17.69-17.93), alumina (5.99-6.06), ferrite (3.25-3.30), lime (64.45-64.85), sulphite (2.70-3.46), loss on ignition (3.32-6.60), free lime (0.36-1.73), particle size [90 microns (0.93-7.07) and 180 microns (0.00-0.80)], Blaine (283-394) m2/kg, soundness (0.67-1.17) mm, consistency (26.27-28.90), Vicat plunger penetration (5.33-6.00) mm, initial setting time (105.33-125.33) mins, final setting time (184.67-191.33) mins, 28 days strength (41.62-50.56) MPa. Statistical analysis revealed that OPC, limestone composite Portland cement containing 5-15 % added limestone and market sampled Portland cement brands all satisfied NIS specifications (28 days strength ≥32.5 MPa, soundness ≤ 10 mm, sulphite ≤ 3.5 %, plunger penetration 5-7 mm and initial setting time ≥ 75 mins) for Portland cement. This indicates that limestone composite cement containing not more than 15 % added limestone could be used for construction work without fear of failure or building collapse.
CHAPTER ONE
1.0 INTRODUCTION
1.1The Nature of Cement
Cement is the widest known building material in the civil industry. Cement is a substance used to bind solid fragments or masses of solid matter together to form one whole substance for the purpose of building, for example in making building blocks and concrete. By this definition the term cement embraces a large number of different substances having adhesive property. However popular use of the term cement has been restricted to adhesives used to bind stones, bricks, tiles etc in the construction of buildings and other civil works1. These are largely adhesives consisting of a mixture of compounds of lime as their principal constituents. These are termed calcareous cements1. Cements of this kind are finely ground powders which when mixed with water set into a hard mass. Setting and hardening result from hydration, which is a chemical combination of the cement compounds with water. As a result of their hydrating properties, constructional cements, which set and harden in the presence of water, are called hydraulic cements. Among these is Portland cement 2. Cement is applied as mortar and/or concrete. Mortar is used in binding bricks, blocks and stones in walls. Concrete is used for large variety of constructional purposes which include road construction and dams. Cement application as mortar or as concrete has helped in solving the durability needs of infrastructure such as houses and offices, roads, bridges etc.
1.2 World Cement Production and Consumption
The need for modern housing has generally increased the demand for cement. Consequently, cement production has grown exponentially over the years. In 2002, the world production of hydraulic Portland cement was 1,800 million metric tons. The three top producers were China with 704 million tons, India, with 100, and United States of America, with 91 million metric tons. These three countries produce about half the world’s total production 3. In 2005, China led with 43.46 percent followed by India producing 6.38 percent, then United States of America with 4.38 percent. For the past 18 years, China has consistently produced more cement than any other country in the world 3. This explains why China has the highest carbon dioxide emission in the world. In 2006 it was established that China manufactured 1.24 billion tons of cement which was 44 percent of the world total cement production 5. Demand for cement in China is expected to advance by 5.4 percent annually and this exceeded 1 billion tons in 2008. Cement consumption in China is expected to hit 44 percent of global demand and China will remain the world’s largest national consumer of cement by a large margin
As the demand for cement increased over the years different types of Portland cement evolved in order to meet the demand. Type 1 or ordinary Portland cement (OPC) is the best cement. It has the highest strength, but it is expensive. Therefore cheaper cements of less strength or quality have been produced. These cements differ in their properties due to the various supplementary materials added to the raw materials, namely; limestone and gypsum. Examples of these supplementary materials include fly ash, pozzolana, slag, condensed silica fume, volcanic ash, rice husk ash, and limestone 7. Countries such as Britain, Spain, France and Argentina based on research results, have set standards for inclusion of supplementary materials like limestone and other pozzolanic admixtures to OPC 7. For example British Standards (BS 882) allows up to 15 % inclusion of limestone to OPC 8.
1.3 Cement Production in Nigeria
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