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CONCRETE TECHNOLOGYwww.cpi-worldwide.com CPI %u2013 Concrete Plant International %u2013 5 | 2025with SANS 5862-1:2006. Where workability fell outside of the design slump of 100 %u00b1 25 mm, a modified polycarboxylate polymer superplasticizer was added. Compressive strength tests were carried out on standard 100 mm cubes cured in a water tank at 23 %u00b1 2%u00baC. Testing was performed at 7 and 28 days in accordance with SANS 5863:2006. Core samples for preparation of Durability Index (DI) test specimens were extracted from 100 mm cubes, cured for 28 days in a water tank at 23 %u00b1 2%u00baC, and were prepared in accordance with SANS 3001-CO3-1:2015. The Oxygen Permeability Index (OPI) test was performed according to SANS 3001-CO3-2. Results and discussions Fresh concrete workability Results of the slump test are illustrated in Figure 2. Before the addition of superplasticizer, none of the mixes achieved the design slump of 100 %u00b1 25 mm. Furthermore, slumps of the 0.45 w/b mixes were lower than that of the 0.60 w/b mixes due to the decrease in free water available to provide adequate workability. Prior to the addition of superplasticizer, slump decreased with the addition of fRCA. This is associated with the increase in water absorption of fRCA in comparison to natural dune sand, as shown in Table 1. Water absorption of fRCA is greater due to the presence of porous HCP phases. Therefore, there is less free water present in fresh concrete to assist with workability. This decrease in performance may have been further affected by the shape of fRCA which is typically more angular and elongated than natural dune sand and has a higher surface area due to the porous cement paste phases [3]. To achieve an equivalent slump, superplasticizer dosage had to be increased with increasing fRCA replacement levels. However, with the addition of superplasticizer, all mixes achieved the design slump. Superplasticizer dosages ranged from 0.31% to 0.87% by mass of binder for the 0.45 w/b mixes and from 0.25% to 0.80% by mass of binder for the 0.60 w/b mixes. All superplasticizer dosages fall within the limits of 0.3% to 3% specified by the manufacturer. Compressive strength The average compressive strength and the associated standard deviation measured at 7 days and 28 days after casting is illustrated in Figure 3. The test results fifffififffflfiffffififfflfiff%u001afiff%u0019fiff%u0018fiff%u0017fiff%u0016fiff%u0015fiffifi%u001afi%u0018fi%u0016fifflfififi%u0014%u0013%u0012%u0011%u0010%u000f flfi%u0014%u0013%u0012%u0011%u0010%u000f %u0019fi%u0014%u0013%u0012%u0011%u0010%u000f fi%u0014%u0013%u0012%u0011%u0010%u000f flfi%u0014%u0013%u0012%u0011%u0010%u000f %u0019fi%u0014%u0013%u0012%u0011%u0010%u000ffi%u000e%u001a%u0019%u0013%u000c%u000b fi%u000e%u0018fi%u0013%u000c%u000b%u0009%u0008%u0007%u0006%u0008%u0005%u0004%u0003%u0001%u0001%u0081%u0007%u0006%u0013%u008d%u008f%u0003%u0004%u0090%u0007%u0013%u009d%u0014%u00a0 %u0005%u0009%u00ad%u0008%u0013%u009d%u00ad%u00ad%u00a0%u0080%u0082%u0001%u0001%u0004%u0005%u0013%u0003%u0005%u0009%u00ad%u0008 %u0083%u0001%u0082%u0004%u0005%u0013%u0003%u0005%u0009%u00ad%u0008 %u0084%u0013%u008d%u008f%u0003%u0004%u0090%u0007%u0013%u009d%u0014%u0013%u008f%u0012%u0013%u000b%u0001%u0082%u008d%u0007%u0006%u00a0Fig. 2: Concrete slump and associated superplasticizer dosage.