Mechanical Properties of Basalt Fiber chopped strands Concrete

PRODUCT  INTRODUCTION

Concrete, as a widely used building material in civil engineering, has good mechanical properties, but with the continuous deepening of the application of engineering technology, the shortcomings of its basic mechanical properties are gradually exposed. Due to the low tensile strength characteristics of only one-tenth of the compressive strength, resulting in members of the tensile process are prone to cracking, which directly reduces the durability of the components, narrowing the scope of application of Concrete Materials. To improve the engineering performance characteristics of concrete and solve the problems in the application of concrete, scholars have been improving the performance ofconcrete materials for many years and have achieved stage-by-stage results, such as the addition of admixtures, adjusting the mixing ratio, improving the production process and maintenance methods.

1. Test materials and test methods

P. O 42.5 ordinary silicate cement was selected, with 28d compressive strength of 48.3MPa and 28d flexural strength of 8.2MPa. medium sand with a fineness modulus of 2.5-2.6 was used as fine aggregate, with an apparent density of 1996kg/m3. continuous graded crushed stone of 5-27mm was used as coarse aggregate, with an apparent density of 2737kg/m3. A water reduction rate of 40% was used. 40% of Sika polycarboxylic acid highly efficient water-reducing agent was used. The length of basalt fiber chopped strands is about 30mm, the diameter of the monofilament is about 15um, the density is 2.7g/cm3, the modulus of elasticity is 95-120MPa, the tensile strength is 3300-4500MPa, and the elongation at break is about 2.5-30.%.

The relevant fits used in this test are shown in Table 1. The compressive test is implemented according to the Standard for Test Methods of Mechanical Properties of Ordinary Concrete. The compressive test adopts 100×100×100mm cubic specimens, 3 specimens in each group, standard curing 28d.

2. Test steps

(1) first wipe the test piece to be tested after checking the appearance and measuring the size, accurate to me. The unevenness of the specimen bearing surface reaches 100mm, the error is not more than 0.5mm, and the bearing surface and adjacent non-perpendicularity should not be greater than the requirements of the degree of 1 degree;

(2) the specimen axis of the test machine aligned with the center of the pressure plate under the test machine. Open the test machine, when the upper-pressure plate and the test piece close, adjust the support, so that the force is uniform;

(3) the loading process to maintain a continuous and uniform, the test loading speed takes 12kN / s-18kN / s; (4) record the maximum load, accurate to 0.1MPa.

3. Test results and analysis

As can be seen from Table 2, the 7d compressive strength of concrete with the increase of Basalt fibers presents the characteristics of unchanged to a gradual decrease, which is mainly due to the addition of basalt fibers, in the fibers and cement formed at the interface to produce a weak surface, and with the increase of the fiber mixing amount, this kind of weak surface continues to increase, so the cubic compressive strength naturally continues to decline. The 28d compressive strength of concrete with the increase in basalt fiber dosage shows a trend of first increase and then decrease, the reason for this first increase is a small amount of dopedbasalt fibers play a role in connecting to a certain extent in reducing the shrinkage deformation of the concrete itself, while at the same time increase the weak surface relative to the 28d strength increase to be a lot less, which in the overall performance of the strength increase.

4. Result

From the perspective of cubic compressive strength, when the shortcut basalt fiber admixture reaches about 1-1.5% by volume percentage, the 7d and 28 cubic compressive strengths of the shortcut basalt fiber concrete are increased to a certain extent as compared to that of the concrete without fiber admixture.