ผลของสารลดน้ำอย่างมากต่อระดับความเข้มของการผสมของซีเมต์เพสต์และมอร์ตาร์ / นิพนธ์ พงษ์ลิมานนท์ = Effects of high range water-reducing admixture on mixing intensity of cement paste and mortar / Nipon Ponglimanon
It has been widely accepted that mixing process will be a major factor that greatly influences to the quality control of concrete mixture. The method to specify the adequacy of mixing process has been an outmost topic interested by concrete industry for a long time. The previous research can be concluded that mixing intensity greatly affects to the properties of concrete after mixing and can be adopted as an indicator to specify the mixing adequacy. Since the study has also been shown that mixing intensity depends on a variety of factors such as HRWRA content, movement of coarse aggregate and properties of powder materials. This research will focus on the effect of mixing energy and mixing intensity of cement paste and mortar with HRWRA. The study have shown that mixing energy of cement paste is greatly affected by particle arrangements and their interactive bonding. For cement paste with HRWRA, it have been found that HRWRA brings cement particles becoming denser; at the same time, it weakens their bonding by the effect of electrical repulsive force. For mortar mixture, the effect of HRWRA affecting to mixing energy must be described in 2 different cases: As the ratio of cement's solid volume to total solid volume is greater than 0.25 and lower than 0.25. For the first case, effect of cement paste is dominant so the effect of aggregate can be omitted; however, the effect of aggregate to particle bonding have to be included in the later case. For the effect of mixing intensity, the study have shown that the optimum mixing intensity of cement paste without HRWRA is independent to the water-cement ratio. Mean while, for cement paste with HRWRA, it can be shown that HRWRA will reduce some particle contacts, so the dissipating energy can be decreased. Furthermore, HRWRA prevents cement to agglomerate by its lubricating effect depending on the distance between cement particle. The study have also indicated that the optimum mixing intensity of mortar both with and without HRWRA varies linearly to the ratio of solid volume fraction of cement to total solid volume in mixture and the optimum mixing intensity of cement paste. For the reason that HRWRA significantly reduces the optimum mixing intensity can be explained by dispersing effect of HRWRA to the cement particle. This surface reaction brings to the less external mechanical energy to be input. However this research does not account for the effect of coarse aggregate movement through the effect of other powders to the mixing intensity. The further studies must be conducted.
