Influence Research Of Fly Ash On Mechanical Properties Of Shrinkage-compensating Shotcrete

Nowadays, shotcrete has became an important modern construction method in the construction of mine engineering and underground engineering. It has many advantages, such as simple process, fast construction, reasonable economy and good adaptablity. Adding expansive agent and fly ash into the shotcrete can not only compensates the concrete shrinkage and decreases the cracks, but also reduces the hydration heat, improves the workability of concrete and cuts the cost. The effect of admixture to fly ash hydration and the basic mechanical properties of concrete are researched through experiment.Four cementitious materials system are considered in microscopic test. They are cement-fly ash, cement-fly ash-accelerating agent, cement-fly ash-expansive agent and cement-fly ash-accelerating agent-expansive agent. Micro morphology and crystal structure of these hydration products at3d and28d are researched by Scanning electron microscope(SEM) and X-ray diffraction(XRD). The influences of two admixtures, expansive agent and accelerating agent, to fly ash hydration are analysed. Results show that fly ash hydration can be boosted by accelerating agent as many hydration products on fly ash particles and no clear interface between them. And there is a little effect of expansive agent to fly ash hydration as no obvious change on fly ash particles.The basic mechanical properties are obtained through an orthogonal test which regards expansive agent content and fly ash content as variables. The fly ash content can be0%,10%,15%,20%,25%,30%,35%and40%, and the expansive agent content can be0%,6%and8%. Compressive strength, tensile strength and flexural strength of concrete at28d are measured by23group tests. Each group contains3specimens. With the fly ash content increasing, the strength of shotcrete only adding fly ash decreases. When the content is more than30%, the decline is more fast. With the expansive agent content increasing, the strength of shotcrete only adding expansive agent first increases and then declines. When the content is6%, the strength is better. Compressive strength of this concrete is3.2%more than that of standard concrete, tensile strength is5.8%and flexural strength is2.0%. For the concrete adding both expansive agent and fly ash, the strength first increases and then declines when the fly ash content is less than30%. When adding6%expansive agent and10%fly ash, compressive strength is4.7%more than that of standard concrete, tensile strength is6.6%and flexural strength is4.0%. While the strength drops when adding more than30%fly ash. Hence, the best content of fly ash and expansive agent in shotcrete are10%and6%respectively.