Effect Of Expansive Agent On Properties Of Concrete

The expansive agent can enhance the impermeability and the cracking-resistance of concrete through the working of the compensation shrinkage of concrete produced by confined expansion when it is added to concrete. Furthermore, the compactness, the strength, and the durability of concrete with the addition of UEA can improve. Despite that, there are different opinions on the application of expansive agent to the actual engineering projects. Their differences mainly result from the following reasons: (1) The concrete with the addition of UEA can not yield expected expansion very often; (2) The concrete with the addition of UEA still cracks in the middle or later period of time, or even in the early period; (3) There are still misgivings about the correlative durability of concrete added with expansive agent, especially its anti-carbonization and its anti-rustiness of the reinforcing steel bar. In order to address the above mentioned problems, this thesis makes a systematic and thorough study of the following aspects: the change of alkalinity of concrete with the addition of expansive agent and its resisting of carbonization and the rustiness of reinforcing steel bar; the influence on expansion rate under restraint of concrete with the addition of expansive agent by different temperatures, different humidity, different water-binding material ratio; and different kinds and content of admixture. Besides, the paper discusses the influence on the stability of ettringite by different temperatures and different humidity and analyzes the reasons and conditions of the delayed formation of ettringite. The study brings about the following findings:①When the content of UEA increases, the alkalinity of concrete decreased slightly. But the decrease is very small, when the content of UEA is below 20%, the value of pH of concrete remains above 12.②With the increase of the content of the expensive agent, the ability of resisting carbonization and rustiness of reinforcing steel bar in concrete is descending, especially when water-binding material ratio is above 0.4, it decreases more noticeably. However, when water-binding material ratio is lower than 0.4, there is no influence on the anti-carbonization and the anti-rustiness of reinforcing steel bar of concrete in spite of the increase of the content of expensive agent.③Temperature and humidity have great influence on the expansive effect of the expansive agent. When humidity is saturated and temperature is under 70℃, with the increase of the temperature the expansion effect in the early period of time is greater while the expansion effect in the middle and later period of time is slightly smaller. When the temperature exceeds 80℃, the expansion effect diminishes greatly with the increase of the temperature due to the stability of ettringite.④The mineral admixtures have some influence on the expansive effect of the expansive agent, but of those the fly ash has the slightest influence. And with the addition of milled slag or silica fly, the expansion effect of the expansive agent is weakened.⑤ The expansion effect of the expansive agent is affected by water-binding material ratio and the expansion effect is relatively small when the water-binding material ratio is low.