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7-i4-04; �7:40 ;Leste� Bulldln8 ;3203955376 # 20/ 28 <br /> Article Request Page Page 18 of 26 <br /> <"�<`:.. o:. � �I <br /> .H�;: <br /> �';�"�� ::S <br /> .i '.s <br /> „ i <br /> �.., r <br /> �n,. <br /> x <br /> � <br /> :�.r:�.. '�Ykz <br /> �'�•r �a��•.�s�p��2� ��` ��'� ��Y <br /> �.x ..:J».'F�-,-.. :� •i�. ���e'li.' <br /> .> •.r <br /> >n' <br /> p p•:. ^ <br /> ..f' a�?. <br /> (a)(b)Figure 17.(a)Excessive spacing between aggregates results in a relatively weak bond <br /> between aggregates. (U)Close aggregate spacing enables hydrating cement particles to form strong <br /> bonds with a�gregatea. <br /> There are three main inteirelated factors that affect aggregate spacing: (1)water content,(2) <br /> aggregate gradation,and(3)degree of compaction.Water content affects aggregate spacing in two <br /> ways. First,excessive water takes up space that could be occupied by aggregate.Because water is <br /> incompressible,the only way aggregate particles can be forced closer together once the space <br /> between the particles has been saturated with water is to remove some of the water. It follows that <br /> too much water reduces concrete strength.Too little water can also reduce strength.This is <br /> evidenced by the plot in figuxe 15.As water is added to a dry mi1c,a viscous paste with some <br /> cohesiveness is formed which makes it more difficult to consolidate the mixture.This is illustrated <br /> by the relationship between concrete bulk density and W/C ratio in figure 16. <br /> Pazticle size distnbution(aggregate gradation)significantly affects aggregate because it is directly <br /> related to fihe total mass of material within a given volume.A poorly graded aggregate(i.e.,one <br /> with similar sized particles)will have a lower density than a well-graded aggregate(i.e.,one with a <br /> good distnbution of pazticle sizes).This is because smaller particles fill the spaces between larger <br /> particles.It is also important to have a sufficient percentage of small particles,as it is the distance <br /> between the smallest particles that dictates aggregate spacing. <br /> Degree of compaction is the third main factor affecting aggregate spacing.The closer that particles <br /> can be brought togetlner by mechanical meams,the stronger should be the bonds between the <br /> particles. <br /> Once one understands the impact of aggregate spacing on concrete strength,the advantage of in- <br /> situ hydration becomes more apparent First,it appears that closer aggregate spacing can be <br /> achieved by compacting dry ingredients instead of ingredients to which a minimal amount of water <br /> has akeady been added(e.g.,the aznount needed for full cement hydration).This statement is based <br /> http://asae.frymulti.com/requeat2.asp?JII�S&AID=14082&CII�1nv2003&w&i=&T=1 6/4/2004 <br />