【作者】 朱倩；

【导师】 李凤兰；

【作者基本信息】 华北水利水电学院 ， 结构工程， 2011， 硕士

【摘要】 随着国内需求的拉动,“十二五”计划的展开,各地公路,铁路等基建的投入日益增大,迫切需要大量混凝土,因而需要大量砂子。为了保护生态平衡,国家已明文禁止擅自开挖天然砂,使得天然砂供量远远不能满足混凝土生产的需求。因此,机制砂的开发就显得尤为重要。生产机制砂过程中不可避免地产生一定粒径小于75um的石粉,清除多余的石粉,使得机制砂满足现行规范要求,需要耗费大量能源,并造成了环境污染。本文提出了区别于传统生产工艺的生产流程,在破碎前增加对岩石整体冲洗工序以严格控制成品砂的含泥量,破碎后即为成品砂,无需冲洗或风选,从而保持机制砂的级配和特性,可以称之为原状机制砂。生产实践表明,在达到规范要求的机制砂颗粒级配和细度模数指标范围内,原状机制砂的石粉含量有较大的波动,因此,开展实验研究了原状机制砂中石粉含量对混凝土性能的影响,以期为混凝土工程施工控制提供研究依据。首先选用石粉含量为3%~16%的岩石破碎原状机制砂,通过试验研究了配制强度等级C30、C45和C60混凝土的可行性,并对石粉含量变化对混凝土拌合物工作性能和混凝土基本力学性能的影响规律进行了探讨。结果显示,原状机制砂混凝土配合比设计中确定水灰比时,可采用系数αa=0.55,αb=0.19。在原状机制砂亚甲蓝值符合建筑用砂规范要求条件下,石粉含量由5%放宽到13%是可行的,即可保证混凝土拌合物的工作性能,又可满足现行混凝土结构设计规范对混凝土基本力学性能的要求。接着对石粉含量分别为3%、7%和13%的C30和C45级原状机制砂混凝土在3 d、7 d、14 d、28 d、56 d、90 d、120 d、150 d和180 d等各龄期内的立方体抗压强度进行了试验研究,分析了石粉含量对强度的影响,得出了180d龄期内的强度发展规律,并提出了C30和C45机制砂混凝土在任一龄期内的立方体抗压强度拟合公式,试验表明,原状机制砂中石粉对混凝土强度的影响与普通机制砂生产中产生的混有一定泥粉的石粉对强度的影响有本质的不同,对于强度等级为C30和C45的原状机制砂来说石粉含量5%这一限值过于严格是不合适的。结合课题组前期研究,利用不同水泥品种、不同水灰比下大量原状机制砂混凝土立方体抗压强度试验研究结果,根据混凝土强度与水灰比间的关系拟合出了原状机制砂混凝土配合比设计中的回归系数:αa=0.5,αb=0.1,并用该强度公式设计出了不同强度等级的原状机制砂混凝土进行验证,实验结果表明,用该公式设计的原状机制砂混凝土基本满足强度与工作性能的要求,可以为原状机制砂混凝土配合比设计提供参考。同时对180d内12组36个机制砂混凝土收缩试件收缩应变进行了量测,分析了机制砂混凝土在标准条件下收缩应变情况及其收缩应变计算公式。结果表明:机制砂混凝土收缩率随龄期均是先增大然后趋于稳定,对于C45机制砂混凝土来说,石粉含量为7%的收缩率最低,3%和5%的基本一致而且最大,其余含粉量的收缩率基本一致,且均处于二者之间。C60机制砂混凝土的收缩率对石粉含量的变化不敏感。机制砂混凝土干缩基本方程采用对数形式拟合精度较高。最后,制作了不同石粉含量的水泥砂浆试件,研究了其宏观力学性能,并采用XRD和SEM电镜等微观测试方法,研究了石粉在水泥砂浆中作用。力学实验结果表明:机制砂配制的胶砂试件的抗压强度、抗折强度都大于相应龄期的天然砂混凝土;同一龄期下,机制砂胶砂试件的抗压强度随着石粉含量的增加而增加,抗折强度先增加后降低。微观观测发现石粉具有:填充效应、活性和晶核效应。在石粉各种效应的综合作用下,砂浆中含有适量的石粉能够促进混凝土强度的增长,这与宏观力学测试结果相一致。更多还原

【Abstract】 With the pulling of domestic demand and carrying out of the "Twelve Five-Year”program, More and more attentions should pay to instructions of highways and railway here and there, which lead to need a great deal of sands to produce heavy concrete. In order to protect ecological balance, a ban on selfishly excavating natural sands has been announced by our country; as a result, natural sand supply is a far cry from meeting demands for producing the concrete. So it is more important to explore machine-made sand. A certain amount of stone power with diameter smaller than 75 micron is brought in process of producing machine-made sand, redundant stone power need being cleaned out to satisfy the national specification requests, thus, a great deal of fuel will be consumed and give rise to environmental pollution. In this paper a new production process different from traditional production process of machine-made-sand is proposed, that is adding the rock whole washing work stage to control silt content of finished products sand before rocks being broken up and after rocks being broken up made it become finished products sand that no washed, consequently, the machine–made-sand which keep in-place is named proto-machine-made-sand. Practice shows that the content of stone power with proto-machine-made sand has a wider fluctuation margin under the range of satisfying the indexes fineness modulus and grading of machine-made-sand according to the specification of current standard. So the stone power content of proto-machine-made-sand how to affect concrete performances was studied through tests in this paper to provide research basis for engineering construction controls of machine-made-sand concrete.Firstly, the proto-machine-made sand with stone powder from 3% to 16% was used to mix the C30, C45 and C60 concrete with high performance and influence regulations that the stone power content act on fresh concrete workability and basic mechanics performance were also studied in the paper. The results showed that the coefficients ofαa=0.55andαb=0.19 can be used when calculate water-cement ratio in the process of mix design with proto-machine-made sand. On condition that the ethylene blue value of proto-machine-made sand according with specification of current standard of Sand for Building, the content of stone power broad from 5% to 13%,which not only can guarantee fresh concrete workability, but also satisfy request for basic mechanical properties of concrete based on the current specification of concrete structure design code.Secondly, the paper introduces a series of test results of grade C30 and C45 concrete mixed by proto-machine-made sand with stone powder in quality content of 3 %, 7 % and 13 %. Based on the experiments of the cubic compressive strength of concrete at different ages of 3 d, 7 d, 14 d, 28 d, 56 d, 90 d, 120 d, 150 d and 180 d, the strength developing regularities of concrete affected by the content of stone powder during the age of 180d were analyzed, and the formula for predicting the cubic compressive strength of concrete with grade of C30 and C45 at any ages was also proposed. It is proved that the effect of stone-powder in proto-machine -made sand on concrete strength is virtually different from that of the stone powder mixed with powdered mud in ordinary machine-made sand, and the limit value of stone powder content lower than 5 % is not suitable to proto-machine-made sand for mixing concrete with grade of C30 and C45.Next, combined with test results of previous period studied by topic team, A quantity of experimental study of the cubic compressive strength of concrete at different cement types and different water cement ratios are used, according to the relation between concrete strength and water cement ratio ,the regression coefficient ofαa=0.5,αb=0.1 belonged to mix design of proto-machine-made sand concrete is fitted, While by using strength formula of that designed machine-made sand concrete with different stone power content and strength grade. The results showed that above formula was used to design concrete can satisfy the requests for strength and workability, thus, it can provide theoretical reference for mix design of proto-machine-made sand concrete.At the same time, concrete shrinkage strain with proto-machine-made sand of 36 specimens of 12 groups is measured, and shrinkage strain change of concrete with age and predicting formulas under the constant temperature and humidity are also analyzed in the paper. Test results showed that concrete shrinkage strain changed with ages from increase to level off. For the machine-made-sand concrete with grade of C45,the shrinkage strain of stone power with content of 7% is least, while the stone power content of 3% and 5% are equivalent and much larger than that, the shrinkage strain of the others are equivalent well and located in medium between them. The change of stone powder content has no significant effect on shrinkage strain of proto-machine-made sand concrete with grade of C60.When logarithmic form adapted to fitting basic equation of concrete shrinkage will obtain a high precision.Finally, cement mortar specimens with different stone power content were made. By using microcosmic testing method of combing with XRD diffract meter and SEM scanning electron microscope, the mechanism of stone power in the cement mortar was studied. Compared with natural colloidal mortar, the colloidal mortar compression strength and flexural strength made up with machine-made sand are both greater than that; under the same age, the colloidal mortar compression strength of machine-made sand increased with adding of stone power and flexural strength first increased and then decreased. Through micro testing method, filling effect, active effect and crystal nucleus of stone power were discovered. Under the synthesis action of various effects from the stone powder, proper stone power can promote growing of strength,which is agreement with macro mechanical experimental results.更多还原