# Intensified Pozzolanic Reaction on Kaolinite Clay-Based Mortar
## 3 Results and Discussion
### Porosity Analysis  
The results of pore structure analysis are shown in Figure 5. The cumulative pore volume of all samples decreases with curing ages (Figure 5d-f). Figure 5a-c compare pore size distributions of the samples with different curing days. It is observed that there are differences in the first peaks of pore diameters depending on SF contents. The first peaks of both Ref and SF_7.5 are formed nearly at 100 nm and are not changed with the number of curing days (Figure 5a,b). On the other hand, the peak of SF_15 is formed at 9 nm, which is approximately 1/10 times compared to the others (Figure 5c). This difference is owing to the physical filling effect by the surplus SF, and it contributed to fine pore structure of SF_15, which will be discussed in detail.  
Figure 4: X-ray diffraction spectra with qualitative analysis of kaolinite clay based mortars.  
Figure 5: _Cont._  
As can be seen in Figure 6 that compares cumulative pore volumes of three samples at 28 days, the extra SF (over 7.5 wt %) is expected to play a role as a filler. Pores of the mortar between 40 and 500 nm in their diameter can be filled with the extra (unreacted) SF, because its size distribution (see Figure 2) coincides with the pore range. Thus, a part of macropores (25 nm-5 \(\upmu\)m) [45] could be effectively filled with the filler, while increasing the volume of the smaller pores (<25 nm). In short, this filling effect led SF_15 to have fine pore structure (Figure 6b).  
The second peak position of the two samples with SF (SF_7.5 and SF_15) are formed at approximately 10 \(\upmu\)m, which is 10 times larger than that in Ref (Figure 5a-c). The pore range of this peak (5-50 \(\upmu\)m) is related to preexisting microcracks and entrained or entrapped air [45]. These pores, which did not change with curing ages, were possibly formed with the change of rheology of the mortar by SF addition [46].  
Figure 5: Porosimetry of kaolinite clay based mortar: log differential intrusions of Ref (**a**), SF_7.5 (**b**), and SF_15 (**c**), and cumulative pore volume of Ref (**d**), SF_7.5 (**e**), and SF_15 (**f**).  
Figure 6: Cumulative pore volume (**a**), and classification of pozzolanic and filling effects (**b**) at 28 days.  
The measured pore volume was divided into four size ranges in Figure 7, on the basis of the international union of pure and applied chemistry system [45]. However, the micropore range was modified from <1.25 nm to <4.5 nm based on the previous studies which have shown that the enhanced pozzolanic reaction considerably changes the pore structure especially below 4.5 nm range [15; 47]. Thus, this modification can help to effectively explain the change of pore structure by the intensified pozzolanic reaction.  
As expected by Figure 5, the proportions of micro and mesopores of SF_15 are significantly higher than those of the other samples, due to the physical filling effect. However, the proportion of micropores of SF_15 steadily decreased with curing age. In particular, unlike the other samples, the first peak of SF_15 was changed to larger size (from 9 to 17 nm) between 28 and 91 days (see Figure 5c). This indicates that the volume of mesopores (4.5-25 nm) of SF_15 were increased due to expansion with curing age. It has been reported that the pores finer than 10 nm mainly affect shrinkage and creep of hardened cementitious materials [46], and also the degree of capillary tension and stress for drying shrinkage is increased with a finer pore system (below 80 nm range in pore diameter) [15; 48]. Thus, this distinct expansion might be attributed to the accelerated drying shrinkage of matrix and resultant micro cracks, as shown in the low W/B (0.25) cement paste with SF (20% of cement) [49].