Influence Of Steam-curing System On The Performance Of Dry Concrete

Based on the steam curing-related parameters and fly ash, this thesis undertook asystematic study on their influence on the compressive strength, permeability, shrinkageperformance and durability of dry concrete, mastered the key technology of steam-cureddry concrete’s preparation, all of which underpinned the heoretical and technologicalfoundation of the production technology of concrete block for the block casting wall.The main achievements were as follows:The early strength of the steam cured dry concrete was significantly higher than thestandard cured dry concrete, increased by169.5%，but its development of late strengthmay retract, fly ash could improve this undesirable phenomenon. At maximumtemperature for80°C, and holding time for8h, the stripping strength of the dry concreteof procuring time for3h、4h were increased by36.6%、39.3%than1h; At holding timefor8h, the stripping strength of dry concrete of maximum temperature of70°C、80°Cwere respectively increased by3.1%and15.0%than60°C, while the28d compressivestrength were reduced by3.0%and4.8%; At maximum temperature of80°C, thestripping strength of dry concrete of holding time for4h、6h、8h and10h wererespectively increased by24.2%、37.2%、45.6%and59.3%than2h, while the28dcompressive strength were reduced by3.6%,4.7%,7.4%and8.7%. The longer restingtime could reduce the adverse effects of steam curing on the strength development ofthe dry concrete; the more thermostat temperature and time, the stripping strength of thesteam cured dry concrete showed an increasing trend, but28d compressive strengthshowed a decreasing trend.Compared with the standard cured concrete, the shrinkage of the steam cured dryconcrete would significantly reduce; A longer rest period, a longer thermostatic period,a higher heating-up rate and thermostatic temperature could reduce the shrinkage,improve its volume stability; and fly ash would increase the shrinkage of thesteam-cured dry concrete.Steam curing would increase the electric flux and28d carbonation depth of the dryconcrete; increasing resting time from1h to3h、4h, the electric flux would decreasefrom2377C to2043C and1989C,28d carbonation depth was reduced by73.3%and80%; increasing constant temperature from60°C to70°C、80°C, the electric flux wouldincrease from1356C to1602C and1805C,28d carbonation depth increased by17.3%and60%; increasing thermostatic period from4h to6h、8h, the electric flux wouldincrease from1281C to1721C and2043C,28d carbonation depth increased by28.9%and42.2%. Fly ash would increase the resistance to chloride permeability and carbonation of the80°C steam cured dry concrete, and the content of20%and30%flyash of the dry concrete would achieve very-low chloride ion penetration level.At a shorter rest period, a longer thermostatic period, a higher heating-up rate andthermostatic temperature, the porosity and average pore diameter would increase, thenumber of pore of＜20nm would reduce, the number of pore of50～200nm and＞200nm would increase, the larger pore would change to the smaller, it would have anadverse effect to the frost resistance of the dry concrete. The content of fly ashincreasing from10%to30%, the total porosity and the average pore size woulddecrease, fly ash could improve the internal pore structure of the80°C steam cured dryconcrete, it could be up to the national requirements of F50.