Study On The Influence Of Specimen Size And Test Conditions On The Capillary Water Absorption Coefficient Of Porous Building Materials

Capillary water absorption coefficient is one of the important wet parameters to characterize the liquid water absorption capacity of porous building materials.At present,the relevant standards for the capillary water absorption coefficient of porous building materials in the test of specimen size and test conditions are unified provisions.However,different porous building materials due to their pore structure difference,causes the water absorbing capacity,capillary water absorption coefficient measurement in the process of material is also sensitive to temperature is different,therefore,to obtain materials of capillary water absorption coefficient using the same test conditions or standards,will affect the accuracy of the capillary water absorption coefficient of materials,test condition change on different properties of porous building materials the influence degree of the capillary water absorption coefficient is unknown.In view of the above problems,this paper studies the widely used capillary water absorption coefficient test methods and the factors that affect the capillary water absorption coefficient in the experiment.Foamed cement(FC),aerated concrete(AAC)and coral sand concrete with different pore structures are selected(SHS)As the research object,through experiments,analyze the influence of specimen size(bottom area,thickness),ambient temperature(5,15,25,35℃),and immersion depth(3,5,8,10 mm)on the capillary water absorption coefficient.Due to the differences in the water absorption process of different porous building materials,this study uses different models(tangent method,double tangent method,fixed time method,Hall model,other models)to process and analyze the capillary water absorption coefficient test results,and obtain various Data processing method of different porous building materials’capillary water absorption coefficient under influencing factors.Through comparative analysis,the influence characteristics of sample size,ambient temperature,and water immersion depth on the capillary water absorption coefficient of porous building materials are obtained.The specific conclusions are as follows:(1)The growth characteristics of water absorption curves drawn by FC,AAC and SHS during water absorption are different.FC and SHS showed a nonlinear increase in stable water absorption stage,while AAC showed a linear increase in stable water absorption stage.(2)Under different thickness(3,4,5 cm),the capillary water absorption coefficient of FC is greatly affected by the thickness.When the material thickness increases from3cm to 5cm,the growth rates of the capillary water absorption coefficients of FC and AAC are about 30.2%and 4.3%,respectively.The value of SHS capillary water absorption coefficient is less affected by the thickness and can be ignored.(3)Under different bottom areas(the bottom areas are 64 cm~2,100 cm~2,144 cm~2,196 cm~2,and the materials are all regular squares),due to the large internal pores of the FC,it is easy to crack and absorb water.The value of the FC capillary water absorption coefficient is affected by the bottom area.Greater impact.When the bottom area increases from 100 cm~2 to 196 cm~2,the growth rate of FC capillary water absorption coefficient is about 40.5%.When the bottom area increases from 64 cm~2 to 196 cm~2,the growth rates of SHS and AAC capillary water absorption coefficients are about 8.1%and 4.1%,respectively.(4)Under different ambient temperatures(5,15,25,35℃),ambient temperature has a great influence on the capillary water absorption coefficient of AAC.When the ambient temperature increases from 5℃to 35℃,the growth rates of the capillary water absorption coefficients of AAC and FC are about 71.3%and 40.6%,respectively.With the increase of temperature,the hydration reaction rate of SHS is faster,and the self-sealing phenomenon occurs earlier due to the dissolution and deposition of internal soluble salt,which leads to the value of the capillary water absorption coefficient decreased by about 4.1%as the temperature increased from 5℃to 35℃.(5)Under different water immersion depth(3,5,8,10 mm),the water immersion depth had a great influence on the value of SHS capillary water absorption coefficient.When the immersion depth increased from 3 mm to 10 mm,the growth rates of SHS,FC and AAC capillary water absorption coefficients were 38.4%,31.8%and 9.1%,respectively.Finally,the weight analysis of the factors affecting the capillary water absorption coefficient of different porous building materials is carried out to provide suggestions on the experimental conditions and data processing methods for the determination of the capillary water absorption coefficient of different porous building materials,such as specimen size,ambient temperature,immersion depth,etc.