Portland cement, cement clinker and heat of hydration of cement Rak Concrete technology 2 Exercise 2

Cement chemistry uses a form of notation which may seem a little strange… Oxides are referred to by their first letter C represents CaO M is MgO and so on, for all the oxides likely to be encountered in cementitious systems.

This is done because it shortens what are otherwise very long names. Alite: Ca 3 SiO 5 in terms of its oxides is 3CaO.SiO 2. The CaO term is shortened to C and the SiO 2 to S. The compound thus becomes C 3 S. Belite: Similarly, Ca 2 SiO 4 is 2CaO.SiO 2, which is shortened to C 2 S. Tricalcium aluminate: Ca 3 Al 2 O 6 is 3CaO.Al 2 O 3. The Al 2 O 3 term is shortened to A and the compound becomes C 3 A. Tetracalcium aluminoferrite: 2(Ca 2 AlFeO 5 ) is 4CaO.Al 2 O 3.Fe 2 O 3. Fe 2 O 3 is shortened to F and the compound becomes C 4 AF.

Portland cement Figure from the book ”Properties of Concrete”, A. M. Neville p. 12. Formation and hydration of Portland Cement

Chemical composition of Portland cement ComponentAbbreviationContent CaO C60-70 % SiO 2 S17-25 % Al 2 O 3 A3-8 % Fe 2 O 3 F0,5-6,0 % MgO 0,1-4,0 % Na 2 O + K 2 O 0,2-1,3 % SO % Mineral composition of Portland cement Portland cement clinker Additives ( GGBS, fly ash, etc.) Gypsum, admixtures The mineral composion of cement can be calculated from the chemical composition

Mineral composition of Portland cement clinker

The Bogue calculation The Bogue calculation is used to calculate the approximate proportions of the four main minerals in Portland cement clinker. The standard Bogue calculation refers to cement clinker, rather than cement, but it can be adjusted for use with cement. Although the result is only approximate, the calculation is an extremely useful and widely-used calculation in the cement industry.

The Bogue calculation

Standard/modified Bogue : C 3 S ≈ 4,07·CaO – 7,60·SiO 2 – 6,72·Al 2 O 3 – 1,43·Fe 2 O 3 -2,85·SO 3 – 4,07·CaO free C 2 S ≈ 2,87·SiO 2 – 0,754·C 3 S C 3 A ≈ 2,65·Al 2 O 3 – 1,69·Fe 2 O 3 C 4 AF ≈ 3,04·Fe 2 O 3 CaSO 4 ≈ 1,70·SO 3

Problem 1

Solution, exercise 1 C 3 S ≈ 4,07·CaO – 7,60·SiO 2 – 6,72·Al 2 O 3 – 1,43·Fe 2 O 3 -2,85·SO 3 – 4,07·CaO free C 2 S ≈ 2,87·SiO 2 – 0,754·C 3 S C 3 A ≈ 2,65·Al 2 O 3 – 1,69·Fe 2 O 3 C 4 AF ≈ 3,04·Fe 2 O 3 CaSO 4 ≈ 1,70·SO 3

Solution, exercise 1 C 3 S ≈ 4,07·64,8 – 7,60·21,08 – 6,72·5,25 – 1,43·2,71 -2,85·2,88 – 4,07·0,96 = 52,3 % C 2 S ≈ 2,87·21,08 – 0,754·52,3 = 21,1% C 3 A ≈ 2,65·5,25 – 1,69·2,71 = 9,3 % C 4 AF ≈ 3,04·2,71 = 8,2 % CaSO 4 ≈ 1,70·2,88 = 4,9 %

Problem 2 Bogue matrix is a 5x5 square matrix. What significance does the element B(i,j) have? Formulate the Bogue matrix and use it to calculate the compound composition of the clinker presented above.

Bogue matrix = =

When formulating the Bogue matrix, atomic and molecular weights are needed

In which the oxide is CaO (in cement chemistry C) and the clinker mineral is C 3 S

=

Solving problem 1 with the Bogue matrix:

Exercise 3. What is the total heat of hydration of the cement presented in exercise 1? How much is the heat production at 3 and 7 days?

Table from the book ”Properties of Concrete”, A. M. Neville p. 39.

The amount of heat produced by the klinker minerals at the ages of 3 and 7 days: Heat of hydration at the age of 3 days: =335J/g*0,523+42J/g*0, J/g*0,093+84J/g*0,082 =257J/g Heat of hydration at the age of 7 days : =377J/g*0,523+84J/g*0, J/g*0, J/g*0,082 =295J/g 1 joule = calories

Problem 4: Three different cement compound compositions and specific surfaces are presented below : Connect the appropriate heat of hydration curve with the equivalent cement and justify (perustele) your answer. A {C 3 S, C 2 S, C 3 A, C 4 AF} = {57,1, 20,0, 7,0, 8,6} %,4840 cm 2 /g B {C 3 S, C 2 S, C 3 A, C 4 AF} = {69,9, 12,7, 1,7, 10,6} %3050 cm 2 /g C {C 3 S, C 2 S, C 3 A, C 4 AF} = {56,2, 19,0, 8,1, 9,4}%3490 cm 2 /g

With cements whose content of C 3 A is typically around 5-10 %, present at these temperatures (at 50 °C) a so called C 3 A peak. When the amount of gypsum is right, this peak can be seen at the begining of the IV phase. The amounts of C 3 A in the cements A, B ja C are A: {C 3 A} = 7,0 % B: {C 3 A} = 1,7 % C: {C 3 A} = 8,1 % I: peak II: peak III: no peak → cement III is cement B

Outlines of cements A and B are similar. However cement A is ground finer and thus reacts more quickly. → cement I is cement A A( I) B (III) C (II)