# Porcelain Tile Polishing Residue in Concrete as an Additive or Replacement for Portland Cement
## 3 Results and Discussion
### Hardened State Properties
#### 3.2.2 Durability Indicators  
Water Absorption by Immersion  
The water absorption results are shown in Figure 6. Systems with the partial replacement of cement by PPR (S10, S20, and S30) showed lower water absorption values than the reference concrete (REF); these reductions were 4.42%, 8.98%, and 5.14% for S10, S20, and S30, respectively. However, concrete S40 obtained similar results to the reference (with an increase of 1.83%). Finally, the concrete with 50% substitution (S50) showed the highest absorption among all composites, 9.27% higher than the reference. In agreement with the results obtained, [PERSON] and [PERSON] [12] performed cement replacement with 25% of the waste; they observed a reduction in water absorption in concrete, relating this behavior to the dense microstructure provided by the pozzolanic reaction with calcium hydroxide generating C-S-H. However, [PERSON] and [PERSON] [19] found that large proportions of replacement by PPR in mortars showed higher rates of water absorption, and for [PERSON] et al. [11], there was an increase in water absorption at higher percentages of PPR in paving blocks. A high content of substitution excessively reduces the amount of clinker, which reduces the C-S-H formation from its hydration, and makes less calcium hydroxide available for the pozzolanic reaction of the residue. In this study, the compressive strength and water absorption results indicated that substitutions greater than 30% had deleterious effects on the hardened concrete performance. Figure 6: Water absorption of the concretes at 28 days. Conversely, there was a reduction in water absorption as the percentage of PPR increased when the waste was used as an additive. This was found to be 7.06% for A10, 12.82% for A20, 15.95% for A30, 20.75% for A40, and 29.63% for A50, compared to that for REF. A similar behavior was reported by [PERSON] [7]. The pozzolanic activity of the PPR associated with the filler effect caused by the particle size of the waste, which is finer than the cement (Figure 1), promoted a greater refinement of the pore structure [9; 17; 19; 21; 44]; this reduced water absorption. In addition, incorporating the fine particles of PPR promotes additional surfaces for the nucleation and growth of hydrates, which forms a more homogeneous microstructure [45; 46]. The water absorption by capillarity results are shown in Figure 7. Samples with cement replacement and PPR addition showed similar water absorption trends by capillarity wherein S10, S20, A10, and A20 showed higher values than the reference concrete. This increase, at 72 h, was 48.25% (S10), 18.42% (S20), 67.54% (A10), and 41.23% (A20). In contrast, contents higher than 20%, both for addition and replacement, led to a decrease in water absorption by capillarity compared to the reference concrete. At 72 h, this reduction was 8.77% for S30; 14.04% for S40; 17.54% for S50; 10.53% for A30; 22.81% for S40; and 30.70% for A50. Similar behavior was reported by [PERSON] et al. [47], where 5-20% PPR incorporation showed higher absorptions, while there was a decrease in water absorption by capillarity for contents higher than 20%. The authors observed that concretes with 30% PPR presented a 49.06% reduction in water absorption by capillarity compared to concretes with 20% of the residue. Water penetration is inversely proportional to the capillary diameter; the smaller pore size of the concrete with PPR resulted in smaller and more interconnected pores, which increased capillary absorption. The decrease in the average pore diameter in the presence of PPR was reported by [PERSON] and [PERSON] [19], because of the effect of pore tortuosity and/or clogging. [PERSON] and [PERSON] [12] obtained similar results and noted that the capillary water absorption in concretes incorporating porcelain tile waste decreased because of the pozzolanic reactions of the pore filling. In the acid attack resistance test, the reference concrete susceptibility and those with intermediate (30%) and maximum (50%) incorporation of PPR were evaluated.