Study On Properties Of Cornstalk Ash-cement Composites

Currently,the use of solid waste as supplementary cementitious materials is low-carbon environmentally and cost-effective,which can reduce the consumption of cement and ease the environmental pressure.As a large agricultural country,China has a large amount of agricultural solid waste and insufficient disposal capacity.Traditional forms of environmental harm such as field incineration and in-situ burial have been abolished,while the agricultural waste can be used to a certain extent by biomass energy power generation and other utilization methods.The content of organic carbon,inorganic silica and alumina in agricultural waste is high,and the ash content after thermal activation has the potential of pozzolanic activity,which is expected to improve the mechanical properties and durability of cement concrete.This paper studied the influence of different thermal activation parameters on the activity of corn straw ash,including calcination temperature(500?,600?,700?),holding time(4 h,6 h)and cooling system(natural cooling,rapid cooling).The optimum process parameters of thermal activation of corn stalk ash were determined as follows:calcining temperature was500?,holding time was 6 hours,and rapid cooling was performed.Corn stalk ash with the highest activity was replaced by cement with 5?15%content and compared with supplementary cementitious materials such as power plant ash,rice husk ash,fly ash and slag,the mechanical properties,durability and microstructure evolution of cement mortar were studied.(1)The addition of corn stalk ash could improve the early mechanical properties of cement,and the increase was up to 24%,and the early mechanical properties were better than those of the samples with other supplementary cementitious materials.With the development of age,the mechanical properties of the samples with corn stalk ash could also be equivalent to those of fly ash and slag with a large amount.(2)The addition of cornstalk ash increased the water absorption rate of cement-based materials,which was about 1%higher than that of conference group.With the increase of the content of cornstalk ash,the water absorption rate changed little.(3)The addition of corn stalk ash could improve the chloride ion permeability resistance of mortar samples,and the addition of corn stalk ash and rice husk ash could reduce the chloride ion permeability coefficient of the samples.The chloride ion permeability coefficient of cement mortar mixed with corn stalk ash was about 9.7×10^-14m²/s,which was about 13.6%lower than that of the conference samples.The chloride ion permeability coefficient of cement mortar mixed with fly ash,slag and power plant ash was higher than that of blank group.(4)Comparing the effects of the addition of different supplementary cementitious materials on the phase composition of cement,it was found that the addition of corn stalk ash could significantly increase the content of C-(A)-S-H in the early amorphous phase of the sample,and the addition of corn stalk ash,rice husk ash and power plant ash could significantly promote the hydration of C₂S with the increase of age.At the same time,this paper studies the synergistic mechanism of corn straw ash composite cement cementitious materials with different dosage.It was showed that when the mass fraction of cornstalk ash substituted portland cement was 0?8%,the early strength of cement mortar mixed with fly ash remained unchanged,but the compressive strength of cement mortar increased steadily at 7 and 28 days,and the growth rate was higher than that of conference group.The raw materials and cement were characterized by hydration heat,TG,MIP,SEM and QXRD.The alkali components in cornstalk ash reacted with active Si O₂ and Al₂O₃ in fly ash to form amorphous gel,which also accelerated the hydration process of C₂S and C₃S in cement and Si O₂ in fly ash,and the C-S-H phase(K-A-S-H).Cornstalk ash was beneficial to the hydration of cement,improving the pore structure of cement stone,and had obvious refining effect on the pores with pore size less than 1000 nm with the increase of curing age.To sum up,as a green and renewable agricultural solid waste material,corn stalk ash has certain pozzolanic activity after thermal activation and cooling treatment,which affected the chemical composition of hydration products inside cement-based materials,improved the pore structure of cement-based materials,and then improves the mechanical properties and durability of cement-based materials.It provides the necessary theoretical basis and support for the engineering application of green renewable agricultural waste in cement-based materials.