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7-14-04; 17:40 ;Lester Bullding ;3203955376 # 21/ 28 Article Request Page Page 19 of 26 on a comparison of the bulk density of in-situ hydrated concrete(2.2+Mg/m3)and that for normally-hydrated concrete with a 0.26 W/C ratio(�1.9 Mghn3). Second,the confinement of a dry mix prior to hydration helps keep particles together during the hydration process and ttris counteracts the hydrostatic pressures that work to drive the particles apart when excessive water is brought into a mix.Third,during the normal hydration process,cement particles begin to giow while the ingredients are still bein�mixed,and these growing particles are surrounded by water. Consequently,the hydrating cement particles aze not in direct contact with aggregates and other cement particles during early stages of hydration,and when there is excessive water in a mi7c,they may make only minimal contact after hydration is complete. Uniformity of Compacted Miz The main advantage that normally-hydra.ted concrete has over in-situ hydrated concrete is that mixing of ingredients after the addition of water helps disperse cement particles more uniformly thmughout the mix. In other words,water serves as a cement-dispersing agent in normally-hydrated mixes.In the case of in-situ hydration,one must rely on the pmper mixing and placing of the dry ingredients,that is,mixing and placing that does not result in the separa.tion of cement,fine aggregates and coarse aggregates.Separation of cement and fine and coarse aggregates can occur as bagged dry mix is transported,as dry mix is taken from the bag and placed into forms/molds, and as it is vibrated or otherwise compacted into forms/molds.Variations in the degree of such separation from footing to footing would explain the higher than expected differences between footing replicates as highlighted in Table 3. Research is needed to assess m�thods for producing dry conerete mixes that will be characterized by a uniform dispersion of cement after being compacted into forms/molds. Such methods include (1)special treatmenta that adhere/attach dry cement particles to aggregate surfaces prior to bagging, and(2)methods to reduce segregation during bagging,transporation and placement of dry concrete mixes. Introdncing Water into a Dry Concrete Miz When in-situ hydration was found to produce concrete with significant stcength during the post uplift resistance study(Bohnhoi�e�al.,2001),one of the main unanswered questions was"Where did the water come from7"More specifically,was the dry concrete mix hydrated by rainwater movitwg down thmugh the ground via gravitational forces,or water drawn into the mix and surrounding area by surface tension(i.e.,capillary action)?It was primarily in pw�suit of an answer to this question that led to the three water treatmenta featured in this study.Water treaiment A was eatablished to provide a situation in which all dry concrete mix would be hydrated via the capillary rise of water.Water treatment B represented a situation in wluch in-situ hydration was prunarily due to water moving downward by gravitational forces.Water treatment C represented hydration by a combination of gravitational flow and capillary rise. Based on averages listed in Table 3 and plotted in figure 14,one can conclude that there was not a significant difference in the compressive strengths of footings subjectsd to water treatments A and thoae subjected to water treatment B.This is not surprising since water treatments A and B produced somewhat similar soil moisture content levels at the various monitored depths(see figiues 8 and 9).'Thie becomes clearer when the sawtooth plots in figure 9 are smoothed. � Similar soil moisture content profiles in tanks 1 and 2 and tanks 3 and 4 can be attributed to a combination of�factors.First, groundwater table heights in tanlcs 1 and 2 were probably only about 5 cm(2 in.)}ugher than in tanks 3 and 4. Second,capiUary fringe depth was approximately , equal to the depth of sand in each tank(i.e.,capillary fringe depth is equal to the total height of capillary rise above the water table).Thus,even though water was not sprinkled on the tops of http://asae.frymulti.com/request2.asp?JID=S&AID=14082&CID=1n�003&v=&i=&T=1 6/4/2004