Building Materials, Third Edition

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resistance to sulphate attack and lowers the ultimate strength, heat of hydration and contraction
during air hardening. The heat of hydration of 865 J/g.

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 is about 8–14% (normally about 9 per cent) of cement. It is
responsible for flash set but generates less heat. It has poorest cementing value. Raising the
C 4 AF content reduces the strength slightly. The heat of hydration is 420 J/g.

g—™—
22g2g
22€
—2g
XBogue developed a method for
calculating the compound composition from the oxide analysis of a cement. This method is
based upon cooling of the clinker at such rate that equilibrium is maintained. Although
equilibrium does not usually obtain in commercial operations, valuable information can be
derived from such calculations. The method is summarized in the following steps and in Table
5.2. An accurate chemical analysis is entered in the first column of the table as shown.

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g



y e—

p2g—y ƒyQCpPyQCePyQC ™2—2 gPƒ2—2gR

g—y TQ(H H(P ™IaI(H ™PaR(W ™QaS(R ™aSI(S ™RaIH(Q

wy Q(H

ePyQ S(S (2(2(2(2( (2(2(2(2( —IaP(P —PaQ(Q

pPyQ Q(S (2(2(2(2( (2(2(2(2( Q(S

ƒ

yP PP(H (2(2(2(2( (2(2(2(2( (2(2(2(2( (2(2(2(2( aPP(H TQ(P2—"(

ƒyQ I(S (2(2(2(2( I(S

s(2v I(P

s(2‚( H(I

p2g—y H(P

s



2v p2wy p2g—y g—ƒyR gRep gQegQƒgPƒ

I(P Q(H H(P P(S IH(T V(U RP QP

Since the ratio of the atomic weight of CaO : SO 3 = 56.07 : 80.065 = 0.70:1, each percentage of
SO 3 combines with 0.70 per cent of Cao to form 1.70 per cent of CaSO 4. Hence, the percentage
of lime required to satisfy SO 3 (= 0.7 × per cent SO 3 ) is recorded as c 1 in column 4 of the table,
opposite CaO; the percentage of SO 3 is also entered in column 4; and the CaSO 4 content is
summed and entered at the bottom of column 4.
Similarly, since the atomic ratios Al 2 O 3 : Fe 2 O 3 = 101.92 : 159.68 = 0.64 : 1 and 4CaO : Fe 2 O 3
= 224.28 : 159.68 = 1.40 : 1, it is evident that each percentage of Fe 2 O 3 enters into combination
with 0.64 per cent of Al 2 O 3 and 1.40 per cent of CaO to form 3.04 per cent of 4CaO
Al 2 O 3

Fe 2 O 3. Therefore 0.64 × percentage of Fe 2 O 3 is entered as a 1 , opposite Al 2 O 3 in column 5, and
1.4 × percentage of Fe 2 O 3 is entered as c 2 , opposite CaO in column 5; the percentage of Fe 2 O 3
is re-entered in the same column; and the percentage of C 4 AF is summed at the bottom.
Since practically none of the magnesia is combined, it is entered as free at the bottom of
column 2.
The total alumina minus a 1 , entered as a 2 in column 6, is available to combine with lime to
form C 3 A in the ratio 3CaO : Al 2 O 3 = 168.21 : 101.92 is 1.65 : 1. Hence, each percentage of this
available alumina × 1.65 is the percentage of CaO required for C 3 A, and it is entered opposite
CaO as c 3 in column 6. Summing quantities in column 6 gives percentage of C 3 A.