Prediction Model for Autogenous Shrinkage of Concrete with Different Type of Cement

Shingo Miyazawa Department of Civil Engineering, Ashikaga Institute of Technology Ashikaga, Japan Ei-ichi Tazawa Research and Development Initiative, Chuo UniversityTokyo, Japan

Autogenous shrinkage should be considered in order to calculate

thermal stress in massive concretelong term deflection in RC memberstime dependent loss of prestressing force(JSCE,1998)Prediction of autogenous shrinkage

c(t)c0(w/c)(t) (10-6) (JSCE, 2002)

Ultimate autogenous shrinkage c0(w/c) 3070 exp{7.2(w/c)} (0.2w/c0.5) 80 (0.5w/c)

Effect of type of cement : =1.0 (OPC) (other type of cement) Development of autogenous shrinkage (t)1exp{a(tt0)b

Prediction Model for autogenous shrinkage of concrete

Experimental Procedures

Materialsriver sandcrushed stone (maximum size: 20mm) polycarboxylic acid type superplasticizer (w/c 0.180.4)air-entraining and water-reducing agent (w/c 0.50.65)

CementC3S (%)C2S (%)C3A (%)C4AF (%)Specific surface areacm2/g)w/cN54218832800.18-0.65H6311884420M443441232400.22-0.50L3052393350

Measurement of autogenous shrinkage before demolding (JCI, 1996)start of measurements : initial set

Dial gauge

100

400

Teflon sheet

Polyester film

Plug

Sample

Polyester film

Mold

Polystyrene board

(mm)

100

Measurement of autogenous shrinkage after demolding (JCI, 1996)Measurements: 1 day, 3 days, 7 days, 28 days, 2 yearsCuring: 20

Test results (1)

- Effect of type of cement on autogenous shrinkage -

w/c=0.22w/c=0.25w/c=0.5w/c=0.4

Autogenous shrinkage of cement paste with various types of cement(Tazawa & Miyazawa, 1992)

p(t) AC3S(t)(C3S%)BC2S(t)(C2S%)CC3A(t)(C3A%) DC4AF(t)(C4AF%)E(Blaine)F (Tazawa & Miyazawa, 1992)i(t) : degree of hydration of mineral compound (%)(Blaine) : Blaine fineness of cement (cm/g2)A, B, C, D, E and F : constantsAutogenous shrinkage of cement paste at age t (10-6) 0.0042(C3S%)0.0049(C2S%)0.125(C3A%) 0.093(C4AF%)0.00015(Blaine)0.90

NHML1.01.20.850.4

Test results (2)

- Development of autogenous shrinkage with time -

w/cAge (days)Strain Effect of w/c on autogenous shrinkage of concrete (OPC)

Age (days)(t)1expattobw/c=0.40c (t) /c (91)

abw/cw/cobs.Cement: OPCobs.Cement: OPC

c(t)c0(t) (10-6) (JSCE, 2002)

Ultimate autogenous shrinkage c0 3070exp{7.2(w/c)} (0.2w/c0.5) 80 (0.5w/c)

Effect of type of cement : =1.0 (OPC)

Development of autogenous shrinkage (t)[1exp{a(tt0)b]

a = 3.27exp{6.83(w/c)}b = 0.251exp{2.49(w/c)}

NHML1.01.20.850.4

(Measured by 15 organizations)Relation between predicted and observed autogenous shrinkage

Conclusions

Autogenous shrinkage of concrete is strongly dependent on type of cement. The coefficient in JSCE model, which describes the influence of cement type, has been determined on the basis of mineral composition of cement.Development of autogenous shrinkage with time is dependent on w/c. The coefficients a and b in JSCE model, which describe the development of autogenous shrinkage, have been proposed as functions of w/c.Autogenous shrinkage calculated form the proposed model was compared with the observed values, and it is proved that the model has adequate accuracy for practical purposes.

(Measured by 15 organizations)

(Measured by 15 organizations)

Figure 1 Influence of cement type on autogenous shrinkage of cement paste.

50010000Observed autogenous shrinkage (10-6)Calculated autogenous shrinkage (10-6)Age: 7, 14, 28, 70 daysOriginal length :24 hours from casting5001000

as(t)1expaob

9191ab1ababab2828B