Effect of grinding on early age performance of high volume fly ash ternary blended pastes with CKD & OPC

Abstract

8This study investigated setting times and early age compressive strength of the high volume fly ash (HVFA) blended 9 pastes prepared with ground materials. The pastes consisted of 60% Fly Ash + 30% Portland cement (CEM I) + 10% 10 cement kiln dust (CKD) and tests were carried out for four different fly ashes. In phase 1, all the constituent binder 11 materials (class F-fly ash, CEMI and CKD) were initially mixed in the relevant proportions and were ground for 12 varying time periods (1, 2 and 4 hours). In phase 2, the CEM I and CKD were mixed and ground for different time 13 periods (1 and 2 hours) and then added to the unground fly ash. Both wrapped and submerged curing were used 14 for compressive strength test samples. Overall, grinding of constituents appeared to be largely ineffective at 15 increasing 2 day compressive strength although strength enhancements at 28 days were generally observed. Paste 16 samples that were made from interground constituents generally achieved higher 28 day strengths than 17 corresponding pastes where only the activators were ground, although this was not consistent throughout so 18 further investigation is suggested in this area. Submerged curing is generally less effective in increasing compressive 19 strength than wrapped curing as leaching of CKD is suspected to have occurred. 20 21

Influence of selected activating methods on hydration processes of mixtures containing high and very high amount of fly ash

“…It may be the effect of better homogeneity. The advantages of intergrinding on separate grinding of the components were also reported by other researchers [73]. Jaturapitakkul et al [79] Influence of selected activating methods on hydration processes... reaction and densification of the structure.…”

“…There are publications discussing effectiveness of this type of activation depending on different factors, such as the kind of fly ash, the way of grinding of dry constituents (separately or intergrinding), using grinding aids, time of grinding, as well as time and temperature of hardening of composites performed with mechanically activated materials, etc. [11,65,69,73,74,78]. For example, Kumar et al [69] concluded that 50-60% of mechanically activated fly ash can be used as clinker replacement and such blended cement exhibits compressive strength and other properties comparable to commercial cement.…”

“…Fly ash grains diameter below 45 lm are beneficial, and using such fly ash as cement replacement can give higher strength results than originally fly ash composed of fractions of different size [73]. Thus, grinding is often proceeded to obtain such particle diameter, e.g.…”

Investigation of different ways of activation of fly ash–cement mixtures

“…Commonly used cements containing fly ash, slag, pozzolans and other components are commercially available [3]. Nowadays, binding ''green'' mixtures containing ecologically friendly non-clinker components arouse interest and they are the subject of research works, e.g., [4][5][6][7][8][9]. Some industry byproducts can be used for this purpose.…”

“…The amount of fly ash used as replacement of cement usually does not exceed 35%. However, composites containing much higher quantity of fly ash in the binding material arouse interest [8,[10][11][12][13][14][15]. Portland cement in lowcement mixtures acts as hydraulic component and activator for fly ash.…”