*3.2. Compressive Strength*

The results of the compressive strength tests at 7 and 28 days are shown in Table 4, including air and water curing. The test results showed that the strength of the water-cured specimens was better than that of the air-cured specimens, which demonstrated that this type of cementless material should be water-hardened. The hardening behavior of the ternary cementless materials was assumed to be due to the Ca-Si-Al colloidal system, and the strength development was due to calcium silicate hydrate (C-S-H) or calcium aluminum silicate hydrate (C-A-S-H) produced by the hydration process, which also supported the hypothesis that cementless materials could be made without alkali activators. The results were consistent with the results of previous tests [10,11]. The strength increased with hydration time, and the 28-day compressive strength of the specimens cured in water reached between 15 and 18 MPa. The cementless material had a specific compressive strength, which benefited a large number of industrial by-products, reduced the cement consumption, and reduced the carbon emissions.


