Mixture Proportioning and Properties of Self-Consolidating Lightweight Concrete Containing Glass Powder

ACI Materials Journal, Sep/Oct 2005 by Shi, Caijun, Wu, Yanzhong

Strength development

The compressive strengths of the five designed SCLC from 1 to 28 days are plotted in Fig. 8. Mixtures SCLC-B09 and SCLC-B10 showed lower 1 day strength than Mixtures SCLC-B06 and SCLC-B07 due to the replacement of 10% cement by volume with glass powder. After 3 days of curing, however, they gained significant strength and reached almost the same strength values as Mixtures SCLC-B06 and SCLC-B07. Mixtures incorporated with glass dust and fly ash exhibited very similar strength development behavior. Mixture SCLC-B08 exhibited the highest compressive strength at all ages due to the high pozzolanic reactivity of GP-4000, as discussed in a previous publication.26

As mentioned previously, the required 28-day compressive strength (f'^sub cr^) for proportioning was around 36 MPa (5200 psi). It can be seen that the actual 28-day compressive strength of designed mixtures ranged from to 37 to 39 MPa (5300 to 5700 psi), which slightly exceeded the designed strength. This is attributed to the pozzolanic reactions between these powder materials and cement hydration products, which was not considered during mixture design. The contribution from pozzolanic reactions to strengths at 28 days is usually very limited, but can be very significant at later ages.

Autogenous shrinkage

The autogenous shrinkage of SCLC is shown in Fig. 9(a). All batches containing glass powders (SCLC-B07 to SCLC-B10) did not exhibit any dimensional changes during the first 5 days, then showed a slight expansion with time. Mixture SCLC-B06 showed a little shrinkage during the first 25 days and then very little expansion afterwards. The autogenous shrinkage of normalweight self-compacting concrete is usually larger than that of normalweight conventional concrete.7,29 The slight expansion in Fig. 9(a) can be attributed to the use of water-saturated lightweight aggregate. Transport of water from the porous saturated aggregate to the matrix is the major reasons for the reduction of autogenous shrinkage in lightweight aggregate concrete. It is reported30 that a replacement of 25% normalweight aggregate with water saturated lightweight concrete could eliminate the autogenous shrinkage.

Drying shrinkage

The drying shrinkage and mass loss of SCLC after 1 and 7 days of initial moist curing are shown in Fig. 10 and 11. It can be noticed that: 1) shrinkages of specimens under two different curing schemes exhibited the similar trend, that is, increased initial moist curing time did not change the values of drying shrinkage; and 2) mixtures with glass powder exhibited higher drying shrinkage than those containing coal fly ash, and the drying shrinkage decreased slightly as glass powders became finer. The higher drying shrinkage may need to be considered in some applications. Many mechanisms for drying shrinkage, including surface tension, capillary tension, and disjoining pressure have been proposed for conventional hardened cement and concrete materials.31 The size and amount of small pores in hardened cement pastes mainly control the drying shrinkage of hardened cement pastes.