Screening And Performance Of Mineral Admixtures For Dry-Mixed Mortar

There is a series of advantages of stable product quality, variety complete, green environmental protection in dry-mixed mortar. At the same time, accumulating of large numbers of industrial solid waste(fly ash, steel slag, coal cinder, etc.) caused serious environmental load, if the industrial solid waste replace part of cement in dry-mixed mortar as mineral admixture because of “particles shape effect”, "pozzolan effect" and "particles fill effect", which have an application value of high-performance and low-cost for dry-mixed mortar development.The cellulose ether, dispersible polymer powder, water reducing agent and defoaming agent was used as chemical additive in traditional cement mortar to preparation dry-mixed mortar in this paper. and the cellulose ether,polymer powder,water reducing agent, defoaming agent the best dosage was 0.15%?0.2%?1.5%?0.15%,according to the influence rule of chemical admixture on dry-mixed mortar performance. Fly-ash,steel slag,blast furnace slag,coal cinder,metakaolin was used mineral admixtures in dry-mixed mortar, and the influence of mineral admixtures on dry-mixed mortar's water/cement ratio,water-retention,setting time,mechanical strength and drying shrinkage strain was discussed, and the influence of mineral admixtures on cement hydration production was researched by scanning electron microscopy and X-ray diffraction. The results show that:1. Blast furnace slag, steel slag and fly-ash can improve the fluidity of dry-mixed mortar, and fly-ash > blast furnace slag > steel slag. Metakaolin and coal cinder have an negative effect on fluidity of dry-mixed mortar, and metakaolin < coal cinder. For improvement of water retention performance, and fly ash > steel slag >metakaolin > blast furnace slag, but coal cinder has significantly reduced water retention performance. For setting time, blast furnace slag and fly ash has significantly retarding effect, steel slag and coal cinder has weak retarding effect, but metakaolin has a significantly accelerate coagulation effect on mortar.2. For 7 d and 28 d compressive strength, metakaolin, blast furnace slag and fly ash dry-mixed mortar have a low 7 d compressive strength and a high 28 dcompressive strength. steel slag and coal cinder have a certain increase on 7 d and 28 d compressive strength, but coal cinder is much less than the steel slag. The improve effect of five mineral admixtures on dry-mixed mortar compressive strength as follows: metakaolin > blast furnace slag > steel slag > fly ash > coal cinder.3. Five mineral admixtures can reduce drying shrinkage of dry-mixed mortar,reduce effect as follows: metakaolin > blast furnace slag > steel slag > fly ash > coal cinder.4. Metakaolin has certain pozzolan activity in 7 d, reacting generates a large number of C-S-H gel with the cement hydration production Ca(OH)2, and the compactness of hydration products have been increased. blast furnace slag and steel slag has a weak pozzolan activity in 7 d, and increasing of hydration products compactness depend on hydration product C-S-H gel and "particles fill effect", and steel slag hydration product compactness is higher than the slag powder. Fly ash and coal cinder hydration activity is poorer, there is no C-S-H gel in the 7 d hydration process of, and cement hydration products structure is loose. 7 d hydration activity of five mineral admixtures as follows: metakaolin > steel slag > cement > blast furnace slag > fly ash > coal cinder.5. Blast furnace slag and metakaolin have a strong hydration activity, there is a large number of C-S-H gel in 28 d hydration products by the pozzolan reaction, and hydration products compactness becomes more stronger. Steel slag hydration products compactness becomes more stronger mainly depend on itself hydration generated C-S-H gel and AFt in 28 d hydration processing. there is no C-S-H gel in the 7 d hydration process of fly ash and coal cinder, and cement hydration products structure is loose. 28 d hydration activity of five mineral admixtures as follows: blast furnace slag > metakaolin > steel slag > cement >fly ash > coal cinder.The influence of five mineral admixtures on dry-mixed mortar's performance and hydration product was comprehensive considerated, and the screening show that:steel slag and blast furnace slag is more suitable for dry-mixed mortar's mineral admixtures, improve effect on dry-mixed mortar will be better when content were30% and 40% respectively.