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7-14-04; 77:40 ;Lester Bulldin8 ;3203955376 # 4/ 28 Article Request Page Page 2 of 26 Introduction Through the years,many post-frame builders have placed dry concrete mixes into post holes and then have backfilled the holes without adding water to the dry concrete mix(i.e.,without first hydrating the mix).When placed in this fashion,it is assumed that water present in the soil permeates into the mix,hydrating and growing cemcnt particles to form a consolidated mass of concrete.Hydration of a dry concrete mix after the mix has been covered with soil is herein referred to as in situ hydration. - In-situ hydration was first used in the formation of entire post footings. Such reliance on in-situ hydration was largely restricted to smaller agricultural and other non-commercial buildings.As average post frame building size increased and engineering became more advanced,fonning post footings entirely out of non-hydrated concrete mix was phased out.Today,in-situ hydration is used (1)in the formation of above-footing collars as part of the post uplift resistance systein,and(2) under precast concrete footing pads to increase the size of the footing.When used under a precast concrete pad,concrete hydrated in-situ need only havc a compressive strength equal to the pressure at the bottom of the precast footing.In general,tlus is a relatively low pressure,and one that a confined concrete dry mix may be able to withstand without being hydrated.It is irnportant to note that whereas infiltration of watet into a soil mass will reduce the bearing capacity of the soil mass, such infiltration wiU increase the bearing capacity of a dry concrete mix. Relying on in-situ hydration of concrete has several advantages.First,concrete can be used in small porbiona as needed(truck deliveries require simultaneous placement of all footings/collazs). Second,water is not required on site.Third,cold weather is not a factor during construction. Fourth,time associated with clea.ning concrete mixing and placement tools is eliminated.Finally, planning is easier as the construction schedule ia not dictated by concrete delivery. Although in-situ hydradon has been"practiced"for well over a quarter century in Wisconsin,it is only used in the construction of agricultural and other cod�exempt shuctures.Before Wisconsin code officials will allow use of in-situ hydrated concrete in code buildings,its properties must be quantified and guidelines/procedures for placement of dry concrete mixes established. In 200I,as a first step toward investigating in-situ hydration,a seriea of concrete collars were allowed to hydrate in-situ as part of a post uplift resistance study(Bohnhoff et.al.,2001). Collars retrieved from posts removed after 6 and 30 weeks of embedment were cored.The average compressive strengths of these cores for the 6 and 30 week embedment periods were 2130 and 24651bf/in2,respectively.Because of these fairly significant strengths,a decision was made to validate the test results with a more controlled laboratory study involving in-situ hydration of the same concrete mix used in the field study. Research Ubjectives The objectives of this study were to: . Deteimine the relative compressive str�ngth of a specific dry concrete mix when hydrated in- situ. . Examine factors affecting the strength of concrete mixes that are hydrated in-situ. Materials and Methods http://asae.fiymulti.com/request2.asp7JID=5&AID=14082&CII�1n�Z003&v=&i�BcT=1 6/4/2004