Maufacturing of Dry Lean Concrete (DLC) Using Portland Pozzolana Cement for the Construction of Concrete Pavements
A. K. Mishra, Sr. Principal Scientist, & Pankaj Goel, Technical Officer, Rigid
Pavements Division, Central Road Research Institute (CSIR CRRI), New Delhi
IntroductionIn recent years, rigid pavements (portland cement concrete roads) are being constructed in many new projects due to added advantages of longer service life, smoother riding surface and little to no maintenance requirement. Government of India is encouraging the construction of cement concrete roads even at village and Municipal levels. The current practices of the construction of cement concrete road for highways in India require a layer of dry lean concrete (DLC) as a base course over which pavement quality concrete slabs rest. It is one of the common and popular cement treated sub-base/base for concrete pavements. DLC is a no slump plain concrete with a large ratio of aggregate to cement. It contains less amount of cement paste as compared to conventional concrete. DLC layer is an important part of modern rigid pavements. The major advantages of using DLC as base layer includes: provision of a uniform and strong support, high resistance to deformation, enhanced load transfer efficiency at joints, proper fixing of form work & proper placement of dowel bar cradles in semi mechanised construction, movement of construction equipments during construction of the roads, all weather construction and finally a reduction in the depth of pavement slab required from the point of view of axle load consideration etc. Now a day, DLC is being also used during rehabilitation and strengthening of existing distressed bituminous roads with white topping. DLC is generally manufactured with ordinary Portland cement (OPC) as per IRC: SP-49: 1998 specification. The specification [IRC SP-49, 1998] advocates use of other cement such as portland pozzolana cement (PPC), portland slag cement (PSC) also in the manufacture of DLC. It sets a requirement of 10 MPa compressive strength of DLC at 7-day. The minimum ordinary portland cement (OPC) content of 150 kg/m3 is prescribed for it. But it does not give details such as cement content, aggregate to cement ratio, moisture content etc. for DLC manufactured with PPC and PSC.
Today, OPC is generally not readily available in open market even in megacity like Delhi. In small towns and cities dealers have to make full payment (1-2 months in advance) to get OPC from its manufacturers. As the supply of OPC in open market is highly restricted, the consumers have no option other than to use PPC. The distinct differences between these two types of cement (PPC and OPC) include the presence of fly ash and much higher value of normal consistence of PPC. Table 1 presents some codal as well as generally encounter values of for the basic properties of OPC and PPC.
About 70% of cement produced in our country is PPC, therefore, the know-how and data generated through the research work will encourage use of correct amount of PPC in the manufacture of DLC. For this purpose, an extensive experimental investigation was conducted to know the amount of PPC, the concrete mix proportions i.e. aggregate to cement ratio and moisture content for the DLC to be manufactured with PPC so that the requirement of IRC: SP-49 specification in term of strength development could be met.
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