Elastic modulus change investigation of cement paste before and after carbonation using nanoindentation technique

The elastic modulus of OPC cement pastes before and after carbonation was tested by nanoindentation technique. The test results show that carbonation reaction causes significant reduction of the frequencies of elastic modulus in the 7∼34GPa and 83∼160GPa, meanwhile a dramatic increase of the frequency of elastic modulus in the 34∼83GPa. Both portlandite, C-S-H gel and unhydrated cement particles are susceptible to carbonation. The elastic modulus frequency value of LD C-S-H and HD C-S-H after carbonation decreases by 85.4% and 55.5%, respectively. LD C-S-H is more heavily affected by the carbonation degradation compared to HD C-S-H. Before carbonation reaction, the size of unhydrated cement particles is about 15∼30um, and the hydrated products wrap around the unhydrated cement particles and the elastic modulus decreases progressively outward from the center of cement particles. After carbonation reaction, the number and size of unhydrated cement particles decreased obviously.