Abstract: Unconfined uniaxial compression test was performed on composite foamed lightweight concrete specimen with wet density of 500 kg/m3 , 800 kg/m3 and 1000 kg/m3 to analyze the effects of two kinds of early strength agent , calcium chloride and sodium sulfate , on the early compressive strength of lightweight composite foamed concrete .Otherwise the Optical microscopy technology and image analysis technology were applied to discuss the effects of calcium chloride and sodium sulfate on the early compressive strength from the micro perspective .The results illustrate that both types of early strength agents affect the early compressive strength obviously .Especially the 3 d, 7 d, 14 d compressive strength increase by at least 44.3%, 25.4% and 11.2%, and the sodium sulfate performs better .The incorporation of early strength agents could make its micro pore structure index improved significantly from the micro perspective ,especially the sodium sulfate .

Key words: early strength agent;foamed lightweight concrete;compressive strength;micro-structure;curing time