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CONCRETE TECHNOLOGY54 CPI %u2013 Concrete Plant International %u2013 5 | 2025 www.cpi-worldwide.comAs with compressive strength results, a two-sample t-test showed that there was no significant difference in the OPI results of mixes with 30% and 50% fRCA replacement levels in comparison to the control mix at both w/b. This suggests that replacement of up to 50% of fine aggregate with fRCA (100% of the dune sand component of the fine aggregate) by mass has limited influence on gas permeability performance of the hardened concrete. However, unlike with compressive strength results, a two-sample t-test also showed that no significant difference was observed between all OPI values, in spite of differences in replacement level and w/b. This is further illustrated by the overlapping error bars shown in Figure 4. The WSI test measures the rate of the movement of a wetting front through concrete under capillary suction (sorptivity) as well as water-penetrable porosity. As in observed in OPI results, a two-sample t-test also showed that no significant difference was observed between all porosity values, in spite of differences in replacement level and w/b. This is further illustrated by overlapping error bars observed in Figure 7. The WSI test is commonly subjected to a relatively large scatter in test results, considering which all WSI results obtained in this study can be seen as equivalent, confirming the above-observed trend, i.e. that the addition of fRCA has had no negative effect on the penetrable pore structure of the concrete. Porosity values observed indicate concrete which may be classified as having poor to good performance (between 10% and 12% as in 0.60 w/b mixes) or good to excellent performance (less than 10% as in 0.45 w/b mixes) [10]. All sorptivity values observed indicate concrete which may be classified between poor and good or good and excellent performance (between 6 mm/h1/2 and 10 mm/h1/2) [10]. Therefore, in spite of the presence of porous HCP, concrete containing fRCA was found to have good durability performance that was comparable to that of control mixes. Conclusions This paper presented an experimental investigation of the effect of replacing natural dune sand with fine recycled concrete aggregates (fRCA) with a maximum particle size of 1.18 mm on the fresh and hardened properties of concrete. Key findings are as follows:%u2022 Workability decreased as fRCA replacement level increased, which could however effectively be counteracted with the use of a superplasticizer. %u2022 Results of compressive strength and durability testing were comparable at all replacement levels, for both w/b ratios. This suggests that replacement of up to 50% of fine aggregate with fRCA (100% of the dune sand component of the fine aggregate) by mass may have limited influence on hardened concrete performance and confirms that the use of fRCA is a viable option for the production of structural concrete. nReferences[1] Peduzzi, P.: Sand, rarer than one thinks. Environmental Development 11, 208-218 (2014).[2] UNEP. Sand and sustainability: 10 strategic recommendations to avert a crisis. United Nations Environment Programme, Geneva, Switzerland (2022). [3] Nedeljkovic, M., Visser, J., Savija, B., Valcke, S., Schlangen, E.: Use of fine recycled concrete aggregates in concrete: A critical review. Journal of Building Engineering 38, 102196 (2021).[4] Angulo, S., Ulsen, C., John, V., Kahn, H., Cincotto, M.: Chemical-mineralogical charac-terization of C&D waste recycled aggregates from S%u00e3o Paulo, Brazil. Waste Manage-ment 29(2), 721-730 (2009).[5] Poon, C.S., Shui, Z.H., Lam, L., Fok, H., Kou, S.C.: Influence of moisture states of natural and recycled aggregates on the slump and compressive strength of concrete. Cement and Concrete Research 34(1), 31-36 (2004).[6] Sosa, M., Villagran Zaccardi, Y., Zega, C.: A critical review of the resulting effective water-to-cement ratio of fine recycled aggregate concrete. Construction and Building Materials 313, 125536 (2021).[7] Evangelista, L., de Brito, J.: Mechanical behaviour of concrete made with fine recycled concrete aggregates. Cement & Concrete Composites 29, 397-401 (2007).[8] Tam, V., Tam, C.: Diversifying two-stage mixing approach (TSMA) for recycled aggregate concrete: TSMAs and TSMAsc. Construction and Building Materials 22(10), 2068-2077 (2008). [9] Pereira, P., Evangelista, L., de Brito, J.: The effect of superplasticizers on the workability and compressive strength of concrete made with fine recycled concrete aggregates. Construction and Building Materials 28, 722-729 (2012).[10] Moore, A., Bakera, A., Alexander, M.: A critical review of the Water Sorptivity Index (WSI)parameter for potential durability assessment: Can WSI be considered inisolation of porosity? Journal of the South African Institution of Civil Engineering 63(2), 27-34 (2021). fifffflffifl%u001a%u0019%u0018%u0017%u0016fi%u0015%u0014%u0013%u0012%u0011%u0010 ffifi%u0015%u0014%u0013%u0012%u0011%u0010 %u001afi%u0015%u0014%u0013%u0012%u0011%u0010 fi%u0015%u0014%u0013%u0012%u0011%u0010 ffifi%u0015%u0014%u0013%u0012%u0011%u0010 %u001afi%u0015%u0014%u0013%u0012%u0011%u0010fi%u000ffl%u001a%u0014%u000e%u000c fi%u000f%u0019fi%u0014%u0012%u0011%u000b%u0009%u0008%u0007%u0006%u0005%u0004%u0005%u0006%u0003%u0014%u0001%u0001%u0008fi%u000f%u001a%u0081%u0014fifffflffifl%u001afi%u001afffi%u0019%u0018%u0017%u0016%u0015%u0014 %u0013fi%u0019%u0018%u0017%u0016%u0015%u0014 %u0012fi%u0019%u0018%u0017%u0016%u0015%u0014 fi%u0019%u0018%u0017%u0016%u0015%u0014 %u0013fi%u0019%u0018%u0017%u0016%u0015%u0014 %u0012fi%u0019%u0018%u0017%u0016%u0015%u0014fi%u0011ffl%u0012%u0018%u0010%u000f%u000e fi%u0011ffifi%u0018%u0016%u0015%u000c%u000b%u000b%u0009%u0008%u0007%u0006%u0018%u0005%u0019%u0004Fig. 6: Sorptivity of hardened concrete at 28 days. Fig. 7: Water absorption porosity of hardened concrete at 28 days.