INCREASING AMOUNT OF MINUS 200 FINES IN PORTLAND CEMENT CONCRETE: 200 MESH FINES IN CONCRETE

摘要

Current specifications utilized for most concrete work in the United States limits the percentage of material passing the number 200 sieve. Historical belief has held that these limitations were necessary in order to produce a quality portland cement concrete. These specifications and beliefs were based on years' of experience with natural sands. As the availability of natural sands has been depleted in many areas of the country, it has become economical to produce stone sand. The process of producing a quality stone sand will generate 8 to 12 percent minus 200 mesh material. For many years, this material was removed from the sand as producers worked to meet specifications which limited the amounts passing the 200 mesh sieve. This process increased the cost of stone sand because a percent of the material was wasted. Additionally, handling and disposing of this 200 mesh material created additional cost and concerns. Current research indicates minus 200 mesh material which is clean, dust of fracture from a quality stone may not be detrimental to portland cement concrete. In fact, increasing the amount of minus 200 mesh material, or micro sand, may well improve the properties of portland cement concrete and be an asset rather than a liability. The mounting evidence toward increasing the amount of 100 and 200 mesh material allowed in portland cement concrete should be acknowledged by specifing agencies. This could result in cost effective fine aggregate for use in portland cement concrete which equals or improves the quality of the finished product.