泡沫混凝土气泡性能与基体材料研究进展

Research Progress on Foam Performance and Matrix Materials for Foam Concrete

泡沫混凝土是近年来广泛研究和应用的保温材料。泡沫混凝土制备过程中气泡性能与基体材料是影响其性能的关键。气泡不稳定及基体缺陷制约着泡沫混凝土大规模推广应用。为了揭示泡沫混凝土气泡和基体对其结构与性能影响,本文围绕气泡性能和基体材料,全面总结和分析发泡剂和稳泡剂的种类及用量,基体材料种类和用量以及纤维、外加剂等研究现状,阐明宏观性能及微观结构关联机制,以期为中国泡沫混凝土材料和建筑节能事业提供有益参考。

Foam concrete can be used as a non-load-bearing structure material due to its low density,high porosity and heat and fire resistance,and foam concrete consists of a foaming agent,water,cement,sand and admixture.Air bubbles generate the pores in foam concrete,and the hydration products of the cement,sand,and admixture form a supporting structure.Foam concrete often involves foam collapse,low product strength and susceptibility to cracking during its preparation and practical use.This review was to reveal the foam property of foam concrete and the influence of the matrix materials on the structure and performance.This review also summarized the types and amounts of foaming agents,foam stabilizers,matrix materials,fibers,and additives,and clarified the correlation mechanism between macro-parameters and performance/microstructure.The property of foam concrete is closely related to its foam performance and matrix materials,and foaming agents and foam stabilizers have a dominant impact on the foam performance.At present,foaming agents mainly include physical foaming agents and chemical foaming agents.Physical foaming agents refer to surfactants or active substances with a high activity,forming bubbles via reducing the surface tension of the liquid and producing a double electrical layer on the surface of the liquid film.Physical foaming agents mainly include rosin resin,ionic,protein and composite.Chemical foaming agents produce bubbles via chemical reactions by adding chemical reagents(i.e.,H_(2)O_(2),Zn and Na HCO_(3),etc.).Rosin resin foaming agents are the earliest and most commonly used foaming agents,but they have problems such as a low foaming ratio and a poor foam stability.Ionic foaming agents increase the bubble foaming ratio.Protein-based foaming agents have higher strength and stability,but have shortages such as higher foaming costs.Compound foaming agents are the fourth-generation foaming agents with synergistic effects and take into account ionic foaming agents.The foaming agent has some advantages like high foaming multiple and good stability of protein foaming agent.As the single-use of foaming agents produces a poor stability of foam and results in a low strength of concrete,the foam stability is used to promote the performance of foam concrete by the foam stabilizing agent with its thickening and increase the viscosity of the liquid film and block drainage.Foam stabilizers can be divided into three categories,i.e.,synergistic foam stabilizers,tackifier foam stabilizers,and nano-solid foam stabilizers.The mechanism of action of the synergistic foam stabilizer is to enhance the adsorption of surface molecules,increase the strength of the liquid film,and reduce air permeability,thereby improving the stability of the foam.Viscosity-increasing foam stabilizers are used to increase the liquid phase viscosity of foam to reduce the bubble drainage rate,extend the half-life,and improve foam stability.Based on the adsorption of nanoparticles at the gas-liquid interface,nano-particles have a good foam stabilizing effect.Nano particles transform the original"gas-liquid"foam into a"solid-liquid-gas"three-phase foam,hindering bubble drainage,thereby improving foam stability and refining bubble size.The matrix mainly composed of cement,mineral admixtures and alkali-activated cementitious materials/geopolymer materials is an important factor affecting the performance of foam concrete.Comprehensive consideration of the cement grade and type,the type and amount of mineral admixtures,and the ratio of activators and solid waste materials of alkali activating materials and geopolymer materials is a key to preparing a matrix with a high strength.In addition,the water-cement ratio(W/C),fiber dosage and admixtures are also a key to improving the performance of foam concrete.Summary and prospects The superior performance of foam concrete has promising applications in the fields of building energy saving,roadbed and mine filling.Although the effects of foaming agents and foam stabilizers on the bubble performance are investigated,the bubble performance by different matrix materials and slurries still needs to be further improved,achieving a synergistic enhancement of matrix and bubbles.The large-volume utilization of solid waste matrix materials in foam concrete is a key to realizing the promotion of foam concrete considering the wide range and low price of solid waste materials.The durability of foam concrete still needs to be systematically discussed.In addition,it is also necessary to conduct in-depth exploration of the green multi-purpose application of foam concrete to provide theoretical and experimental supports for the high-quality development of building materials.