硅酸盐学报

西部盐渍土地区中的腐蚀离子严重影响了混凝土的耐久性，在混凝土中加入玄武岩纤维(BF)可减少初始缺陷，延缓腐蚀离子进入混凝土内部的速度，从而改善混凝土的耐久性。基于西部盐渍土环境，对不同BF掺量的玄武岩纤维混凝土(BFRC)在Na_2SO₄侵蚀和冻融循环耦合作用下的宏观性能和微观变化进行研究，并采用有限元软件ABAQUS对试验进行模拟，分析试验过程中BFRC内部应力场、应变场的变化规律。结果表明：BF的加入明显降低了混凝土在Na_2SO₄溶液-冻融循环过程中质量、相对动弹性模量、抗压强度、劈裂抗拉强度的损失率。在冻融过程中BF起到传递和分散应力的作用，使混凝土内部应力重分布提高了混凝土的抗盐冻性能，掺量0.3%(体积分数)时BFRC抗盐冻性能最佳。该有限元模型直观有效地反映出BF在混凝土冻融损伤演化过程中的重要作用。

Introduction On the Loess Plateau in western China,there exists a large number of saline soils,most of which contain salts,typically of sulfate and chloride salts.Since the sulfates in saline soils are sensitive to temperature changes,they are susceptible to salt crystallization expansion and frost heave at low temperatures,which can lead to destruction of concrete structures.Salty soils and freeze–thaw environments cause concrete to be subjected to the coupled effects of simultaneous sulfate attack and freezing and expansion,which further increases the deterioration degree of concrete and seriously threatens the durability of concrete in this area.Adding fibers to concrete can effectively inhibit the plastic shrinkage cracking and improve the durability of concrete such as wear resistance,impermeability and frost resistance.Basalt fiber (BF) has excellent properties such as high strength,light weight,high temperature resistance,high elastic modulus,fracture resistance and corrosion resistance,and it is easy to disperse in concrete and has excellent cooperative work performance with concrete.Therefore,in this paper,the durability of concrete is improved by incorporating an appropriate amount of BF into the concrete to reduce the initial defects and slow down the rate of corrosive ions into the interior of the concrete.Furthermore,the effect of different BF admixtures on the relative dynamic modulus of elasticity,mass loss,compressive strength,and splitting tensile strength of concrete during salt freezing were investigated.The effect of the included BF is also clarified.Methods The concrete was prepared by P·O 42.5 ordinary Portland cement,II grade fly ash,5–20 mm continuous graded gravel and natural river sand fineness modulus of 2.83.The volume content of basalt fiber was 0%,0.1%,0.2%and 0.3%.The test was carried out with reference to the quick-freezing method in GB/T 50082—2009‘Test method for long-term performance and durability of ordinary concrete’,using HC-HDK9/Y type fast freeze–thaw cycle tester.According to the content of corrosive ions in saline soil in western China,Na_2SO₄ salt solution with a concentration of 23 g/L was selected for freeze–thaw cycle test.The loss rates of mass,relative dynamic elastic modulus,the compressive strength and splitting tensile strength during the test were tested.At the same time,Numerical simulation tests were carried out using finite element software ABAQUS to analyze the changes of internal stress and strain fields of basalt fiber reinforced concrete (BFRC) during the tests.Results and discussion The mass and relative dynamic elastic modulus of BFRC under the action of Na_2SO₄ solution-freeze–thaw cycle raised first and then decrease with growth of the number of freeze–thaw cycles.The compressive strength and split tensile strength decrease with the increase of the number of freeze–thaw cycles.The addition of BF slows down the formation of corrosion products and expansion products.Under the same number of freeze–thaw cycles,the addition of BF reduces the generation of microcracks in concrete and prevents crack propagation.The addition of BF improves the freeze–thaw resistance of concrete in Na_2SO₄ solution.And the freeze–thaw resistance performance gradually improves with the increase of the BF volumetric doping within the range of 0.1%to 0.3%.Moreover,the best performance of freeze resistance in Na_2SO₄ solution is achieved when BF doping is 0.3%.The internal stress and strain fields of BFRC with different BF dosage during Na_2SO₄ solution-freeze–thaw cycle test decrease with increasing the BF dosage.At the same BF dosage,the stress and strain increase with increasing the number of freeze–thaw cycles,and the dynamic numerical simulation was in good agreement with the experimental results.Using the‘equivalent temperature load’method,the salt solution-freeze–thaw cycles test process can be effectively simulated by ABAQUS finite element software.The numerical simulation results also show that the stress field of concrete and BF as well as the strain field of BFRC have changed,and that BF plays the role of transferring and dispersing the stresses during the freeze–thaw cycling process,which leads to the phenomenon of stress redistribution inside the concrete,and improves the salt-freezing resistance of concrete.Conclusions In this work,the macroscopic properties and microscopic changes of BFRC with different amounts of BF were studied under the combined effect of Na_2SO₄ erosion and freeze–thaw.The main conclusions are that the addition of BF significantly reduces the loss rate of concrete mass,relative dynamic elastic modulus,compressive strength and splitting tensile strength during the freeze–thaw cycle of Na_2SO₄ solution.BF can transfer and disperse the stress,so that the stresses are redistributed inside the concrete during the freeze–thaw process,thus improving the salt-freeze resistance of concrete.In addition,when the BF content is 0.3%,BFRC has the best resistance to Na_2SO₄ salt erosion-freezing performance.Meanwhile,BF shows an important effect in the evolution of freeze-thaw damage evolution of concrete,which can be visualized effectively by finite element model.