The compression strength characterized using a manual device and a more sophisticated device showed different results even though the trend is similar (Fig. 7). Flexural strength results are better measurements and distinguishable when a more sensitive sensor is used at 3, 7, and 28 days.
Compressive strength properties are similar to the flexural strength as previously discussed.
At 0.2% sodium lignosulfonate, there is an indication that bonding with water is higher than at 0.1 and 0.3% (Fig. 7) indicating that 0.2% sodium lignosulfonate in the mortar was the optimum additive level. The results of this particular determination again showed that sodium lignosulfonate derived from hardwood is better than the commercial sodium lignosulfonate. United States patent (Willy, 1981) shown that ASTM C270 mortars in the laboratory using cement type 1, 35 % and flow 107% flow, had compressive strength of 82.3 kg cm2 for 7 days and 131.1 kg cm at 28 days. In building constructions, the same cement needed 53.4 kg cm2 in 7 days, and 69.6 kg cm2 at 28 days.
Thirteen samples composed of cementitious mortar, grout and concrete had a density of 90 to 161 pcf and a compressive strength of around 640 to 1400 kgf cm2 (Charles et al, 1982). According to Rixom and Mailvaganam (1999), the relationship between the slump and the water-cement ratio for
Mechanical properties of the mortars (flexural and compression strengths) as discussed previously were further verified with a visual method. The results of scanning electron microscopy (SEM) on after-heated specimen clearly show that, the mortar without NaLS as additive, has a rough surface due to flocculation and void spaces left by evaporated water (Figure 8a). Figure 8b definitely shows a smooth and homogeneous surface of mortars containing hardwood NalS. Water dispersion in the mortar is aided by a proper dispersant. This property is consistent with all mechanical properties tested in this experiment.