Studies On Volume Stability Of Steam Curing Foam Concrete

Foam concrete is manufactured by incorporating pre-formed form,generated from foaming fluid by a physical method,to cement paste or a mortar.Nowadays,foam concrete are widely utilized as precast walls for its low density,excellent heat-resistance and sound-insulation,which will do a lot to material and energy saving and respond to the China's sustainable development policy.At the same time,because of its internal porous medium,the early-age strength of foam concrete is too small to demould at half of the day.So steam curing is applied to improve the 12 h strength of Foam concrete.Besides,because lacking coarse aggregate that limits contraction,the volume deformation of foam concrete is too large,which lead to cracks and size deviation in the prefabricated walls.So this paper aims to investigate the Factors affecting the volume stability of foam concrete.Firstly,in order to alleviate the environmental pollution and cut down the prices of prefabricated walls,two kind of mineral materials,fly ash and coal gangue,were added to foam concrete at a ratio of 10%-40%and 10%-50%.When samples were standard cured,strength and shrinkage were both decrease when adding fly ash or coal gangue.However,the optimum amount of samples when steam curing at early ages is 20%for fly ash and 30%for coal gangue.XRD and FTIR were applied to investigate the phase composite and results shows that Ca?OH?₂ were consumed to form C-S-H when curing in steam.And steam-curing can accelerate the progress of cement hydration and pozzolanic reaction.However,the challenge of foam concrete's application is usually its low strength for its porous matrix and reaching the required demoulding compressive strength takes much more time than ordinary concrete.This paper aims to improve the early-age strength of foam concrete by steam curing and an orthogonal matrix was adopted in this research to investigate the influence of the following steam curing factors:preset temperature,preset time,curing temperature and the amount the amount of early strength agent on 12 h strength.The results showed that the best steam-curing system that can yield the highest 12 h compressive strength is 25?for 4h?precuring?+50?For 8h?steam curing?+1.5%Na₂SO₄,which improved the 12 h strength form 0.5MPa to 2.3MPa.And long term strength?28d?and deformation during steam-curing was also investigated.The results show that improving early age strength too much will lead to a deficiency of later-age strength growth.MIP shows that elevated temperature in steaming curing and the short precuring period made the hole of the specimen deteriorated with the relatively large porosity,more big hole,less small hole and irregular shape.Finally,factors including density,standard curing time,humidity,steam curing system was concluded to investigate the mechanism influencing drying shrinkage and volume change during drying-wetting cycles.The results illustrated that the smaller the bubble content and the greater the density,the smaller the shrinkage will be.And higher humidity and prolong of the curing age will decrease shrinkage too.When samples applied to higher steam-curing temperature,the smaller the drying shrinkage.The deformation of samples adjusted to dry-wet cycles shows that mineral admixtures do better to volume stability.Finally,based on Kelvin theory and Yang-Laplace theory,the shrinkage model was put forward.