Abstract
Assessment of 28 days strength from accelerated strength (1 day) can be extremely helpful. Early prediction of 28 days compressive strength is required basically for two purposes. First, to finalize the concrete mix proportions in the laboratory and secondly, for quality control purpose during construction. Through this concept designers can easily identify the uncalculated errors during mix design or variations in materials and exposure conditions etc. and take necessary correction and modification measures to attain the desired strengths at 28 days. As per IS: 9013 methodology to predict the 28 days strength of concrete from accelerated cured strength are indicated only for normal/control concrete. In the past few year focus has shifted from Ordinary Portland Cement (OPC) to Portland Pozzolana Cement (PPC). Fly ash is also being used widely at sites as replacement of OPC. However, there is no such guideline available by which the assessment of 28 days strength of Indian fly ash concrete can be made from accelerated strength tests. In the present study an attempt has been made to predict the expected 28 days compressive strength of concrete having PPC or OPC with fly ash using accelerated temperature regime methods. The experimental study includes the use of 2 brands of PPC, 5 brands of OPC and 2 sources of fly ash for replacement of OPC ranging from 20% to 45 %. Two temperature regimes 900C and 820C were used for accelerated curing. The samples were cured for 7.5 hours and 20hours respectively in each regime for expected 28 day compressive strength. The mathematical equations to estimate the 28 days compressive strength of concrete, cured at 900C for 7.5 hours for mixes having PPC, OPC mixed with fly ash 20% to 35% is fexp28 = 1.223 facs +2.024. The mathematical equations to estimate the 28 days compressive strength of concrete, cured at 900C for 7.5 hours for mixes having PPC, OPC mixed with fly ash more than 35% and up to 45% is fexp28 = 0.993 facs + 6.044.
Highlights
According to Indian Standard acceptance and rejection of any type of concrete should be done by determining 28 days compressive strength (IS- 456, 2000)
The mathematical equations to estimate the 28 days compressive strength of concrete, cured at 900C for 7.5 hours for mixes having PPC, Ordinary Portland Cement (OPC) mixed with fly ash 20% to 35% is fexp28 = 1.223 facs +2.024
The mathematical equations to estimate the 28 days compressive strength of concrete, cured at 900C for 7.5 hours for mixes having PPC, OPC mixed with fly ash more than 35% and up to
Summary
According to Indian Standard acceptance and rejection of any type of concrete should be done by determining 28 days compressive strength (IS- 456, 2000). Potential strength of fly ash concrete may develop at 90 days or even after 180 days (Tokyay, 1999). It is known that the strength of normally cured concrete at 28 days is considered for structural design. This time difference may lead to loss of valuable time and money. For the prediction of 28 days strength of fly ash concretes no such correlation is available. In this current paper provides some strength prediction models have been proposed (Jayanta and Jaydeep, 2016)
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