| In order to meet the requirements of energy saving,green and environmental protection in engineering construction,the research of using plant biomass as raw materials for engineering construction has become one of the hot issues in recent years.Pinaceae plants are widely distributed in mountainous and high-altitude woodland areas in my country.The leaves(pine needles)of Pinaceae plants have the advantages of renewable,large number,and environmental protection,and have the potential to develop into local natural plant fiber building materials.However,the actual utilization rate of pine needle fiber is low at present,and there is no relevant research on mixing pine needle fiber into the concrete.This paper uses Masson pine needle fiber(MPNF)to study the preparation method of MPNF concrete and the influence of MPNF on the short-term and long-term mechanical properties of concrete to demonstrate the feasibility of applying MPNF to concrete.It is suitable for mountainous and high-altitude areas.The development of local characteristic natural plant fiber building materials provides a theoretical basis.First,the MPNF is processed into a length of 30 mm and then immersed in 2% Na OH solution,boiling water and unheated water respectively.The treated MPNF is mixed with new concrete at 0.5%,1%,1.5% and 2% of the concrete volume.By mixing concrete,68 sets of cube specimens and 17 sets of prismatic specimens were produced.Then,mechanical performance tests were performed on the specimens with 28-day standard curing and 200-day natural aging.Industrial CT(ICT)and nuclear magnetic resonance were used to observe the three-dimensional distribution and pore structure of MPNF in each pretreatment method.The relationship between mechanical properties.The main test results are as follows:(1)MPNF after pretreatment can improve the short-term mechanical properties of concrete,and at the same time can ensure the mechanical properties of concrete after long-term natural aging.The best pine needle fiber pretreatment method is 2% Na OH dilute alkali solution soaking treatment,and the fiber content should be controlled within 1.5%.(2)Incorporating MPNF will cause aggregation on the top and bottom of the concrete specimen.As the amount of fiber increases,the aggregation phenomenon becomes more obvious,and this aggregation phenomenon will have an adverse effect on the mechanical properties of concrete.The mechanical test results of concrete specimens show that the degree of fiber aggregation is negatively related to the 28-day mechanical properties of MPNF concrete.(3)The pore structure has a great influence on the mechanical properties of MPNF concrete.The test results show that the mechanical strength of MPNF concrete specimens decreases with the increase of porosity.Among them,the porosity of the test specimens treated with dilute alkali is lower than other specimens,which explains why the mechanical strength of specimens treated with dilute alkali is higher than that of other pretreatment methods. |
