| The popularization and application of low carbon alkali-activated foamed concrete can meet the needs of energy-saving buildings,thereby easing the energy shortage problem,as a kind of inorganic porous lightweight concrete material with high early strength,excellent thermal insulation,high temperature resistance and corrosion resistance.,it can make full use of solid wastes such as slag,fly ash and recycled micro-powder,and is regarded as an environmentally friendly green and low-carbon building material.Firstly,the alkali foams were prepared by diluting different kinds of foaming agents with alkali activators to evaluate the stability of the alkali foams.The effects of activator modulus and alkali equivalent on the stability of different types of alkali foams were studied,and the alkali-activated slag-fly ash/recycled brick powder foamed concrete was prepared by foaming agent with good stability.Secondly,the early stability of fresh foamed concrete of alkali-activated materials was monitored and parameterized by laser displacement sensor.Finally,the macroscopic properties and microstructure of alkali-activated slag-fly ash/recycled brick powder foamed concrete with different activator modulus,alkali equivalent,proportions and types of cementitious materials were studied,and the influential mechanism of various influencing factors on foamed concrete of alkali-activated material was revealed.The main conclusions were drawn as follows:(1)The addition of alkali activator accelerates the condensation and coarsening of bubbles,leading to the acceleration of foam drainage rate,the decrease of foaming multiple,the increase of bubble group density,the increase of bleeding rate,which reduces the stability of foam.Compared with plant foaming agent and animal foaming agent,the foams prepared by compound foaming agent have the highest stability in alkaline environment.(2)The settling time-varying behavior of the alkali-activated slag-fly ash/recycled brick powder foamed concrete paste is closely related to its early stability.With the evolution of time,the paste reaches its critical settling time and critical settling distance.Meanwhile,the settling rate decreases gradually and the critical settling time is earlier than its initial setting time.The increase of alkali activator modulus and alkali equivalent leads to the gradual deterioration of the early stability of alkali-activated slag-sly ash/recycled brick powder foamed concrete,which is manifested in the increase of the critical settling distance,the decrease of the critical settling time,and the acceleration of the average settling rate.The early stability of alkali-activated slag-recycled brick powder foamed concrete is stronger than that of alkali-activated slag-fly ash foamed concrete with the same activator combination and cementitious material ratio.(3)Alkali-activated slag-fly ash/recycled brick powder foamed concrete has good mechanical properties when its alkali activator modulus is 1.2.With the increase of alkali equivalent,the strength of alkali-activated slag-recycled brick powder foamed concrete gradually increases,while the thermal conductivity and connected porosity gradually decrease.With the increase of the content of recycled brick powder,the compressive strength of alkali-activated slag-recycled brick powder foamed concrete gradually decreases,and the thermal conductivity decreases first and then increases.When the content of recycled brick powder is 30%,the thermal conductivity of alkali-activated slag-recycled brick powder foamed concrete is lower.The thermal insulation property of alkali-activated slag-recycled brick powder foamed concrete is better than that of alkali-activated slag-fly ash foamed concrete.According to the pore structure and SEM results,alkali-activated slag-fly ash foamed concrete and alkali-activated slag-recycled brick powder foamed concrete have similar hydration products,and the foamed concrete with more uniform pore size distribution has lower thermal conductivity.The average pore diameter and roundness of the alkali-activated slag-fly ash/recycled brick powder foamed concrete gradually enlarge with the increase of the alkali activator modulus and alkali equivalent.The foamed concrete with low alkali activator modulus and low alkali equivalent has more small holes and round holes. |
