Development and Testing of Geopolymer Mortar
3.2 Experimental Investigation
3.3.2 Workability
The setting time of GPM was found to be much lower than that of PCM. Initial setting time of PCM mix, CM1 was 95 minutes and final setting time was 265 minutes. In some of the GPM mixes, the initial setting time was found to be lesser than that recommended in the IS 8112 2013 [114]. However, addition of admixture and alteration of alkali activator concentration led to enhanced initial setting time. The final setting time was significantly less than the maximum values in all the mixes which makes GPM a strong contender for recognizing it as a concrete repairing agent.
Chapter 3 Development and Testing of Geopolymer Mortar
can be attained. The steep rise of FI curve beyond 20 % FA content point indicated that increase in FI with increasing FA content was more for mixes with FA content higher than 20 %. This trend was exhibited by mixes with both a/b ratios. Increase in addition of FA increases the availability of smooth and spherical particles in the mixes which contribute to better sliding among the particles and reduction of friction which is otherwise caused due to presence of angular UGGBS particles. FESEM images in Fig. 3.11 show the particle shape and distribution in mixes. As FA content in the mixes increases, reduction of total friction among the particles occurs leading to better workability.
Figure 3.20: Effect of FA content on workability of GPM mixes for a/b of 0.6 and 0.65
Addition of SP (both SN and PE based) contributed towards increasing workability of the mixes with constant FA content of 30 % (see Fig. 3.21). Both the types of SP helped in releasing the liquid component in the mixes trapped in flocs by dispersing the solid particles.
It is worth mentioning that the trend of increase in workability with the addition of higher dosage of SP changed for dosage between 1.5 to 3 %. At 0.5 % and 1.5 % SP dosage, mixes with PE based SP showed improved workability, on the other hand mixes with SN based ones showed higher FI at SP dosage of 3%. Such behaviour of mixes with SN and PE based SP have also been observed by Laskar and Bhattacharjee [110] in their work on FA based geopolymeric mixes consisting of SP. At SP dosage of 3 %, solid particles in the mixes got highly dispersed causing separation of semiliquid phase from the solid phase. Such segregation phenomenon was more prominent in mix with SN based SP. It is presumed that
0 20 40 60 80
0 10 20 30 40 50
Flow index (%)
FA content (%)
0.6 0.65
this phenomenon has also caused the high retarding effect in the mix due to 3% SN based SP as seen from results in Fig. 3.15. Thus, it can be said that at very high SP dosage, SN based SP disperses the solid particles in mixes more than PE based SP but this also result in segregation.
Figure 3.21: Effect of SP type and content on workability of GPM mixes.
The effect of change in alkali concentration on workability of mixes with constant FA content of 30 % and SP (both SN and PE based) dosage of 1.5 % is shown in Fig. 3.22.
Increase in alkali concentration reduced the workability of the mixes. By increasing the alkali concentration, total solids in the solution was increased which resulted in more viscous alkali activator and caused obstruction to mobility of particles in the mixes. This resulted in decrease in workability. Such happening was also observed by Palacios and Puertas [115] while working with different types of SP in slag based geopolymeric mixes. The reduction in workability was higher for mixes with PE based SP. Addition of PE based SP to the mix with alkali concentration of 14 M caused formation of a very thick and viscous liquid phase in the mix which was not observed in other mixes. Therefore, it can be said that higher alkali concentration caused modification of chemical structure of PE based SP rendering it ineffective in improving the workability of the mixes. A steep fall of FI has been observed due to increase in alkalinity beyond 10 M for mix with PE based SP. But, for mixes with SN based SP, the fall was gradual and less steep than that of PE based SP ones. Henceforth, it is
0 20 40 60 80 100 120
0 0.5 1 1.5 2 2.5 3
Flow index (%)
Superplasticizer content (%)
SN PE
Chapter 3 Development and Testing of Geopolymer Mortar
understood that PE based SP can be used at alkali concentration upto 10 M without much loss of workability. As elaborated by Laskar and Bhattacharjee [110], this behaviour of geopolymeric systems donot lineup with that of PC based systems when alkali concentration is high. The mechanism related to this behaviour is not known so far.
Figure 3.22: Effect of alkali concentration on workability of GPM mixes.
The mixes with Type I SP addition proved to be the most workable among the other types of SP addition. Flow indices of GPM mixes GM19, GM20, GM29, GM30, GM31 and GM32 are given in Table 3.3. When PE based SP was directly added to NaOH solution, appearance of the solution changed from transparent to whitish colour indicating some chemical change in the solution. Type I and III SP addition showed similar trend of workability affect. Mixes with SN based SP exhibited lower FI compared to PE based SP ones unless it is added to the mix by addition in the alkali activator directly.
Table 3.3. Effect of SP addition type on workability.
Mix SP addition type Flow index
GM19
Type I 74.67
GM20 83.67
GM29
Type II 62.33
GM30 50.67
GM31
Type III 45.67
GM32 64.33
0 20 40 60 80 100
8 10 12 14
Flow index(%)
Alkali concentration (in molar)
SN PE