**7.2 Rapid chloride permeability**

Rapid chloride permeability test (RCPT) is an important test to ascertain the durability of concrete. In this test, as per ASTM C 1202-19 [60], the higher the charge passed through the samples, the concrete is more permeable. The penetration of chlorides through the concrete can affect the reinforcement steel, and the corrosion takes place. Hossain and Anwar [39] studied the rapid chloride penetration of lightweight concrete samples of 20 and 28 MPa compressive strength at 28 days made of waste foundry sand and volcanic ash from Papa New Guinea and reported that the chloride permeability of lightweight concrete decreases with the increase in the percentage content of waste foundry sand. As per the observations of Siddique et al. [57], for 20 and 30 MPa characteristic compressive strength concrete with regular sand partially replaced with spent foundry sand, the charge passed was found to be decreasing with the increase in spent foundry sand content in the concrete mix. In some cases, the chloride permeability decreases up to a certain percentage of used foundry sand in the concrete mix, and further, it increases. Singh and Siddique [31, 56] reported that the chloride permeability of concrete incorporating waste foundry sand decreases up to 15% substitution of fine aggregate with waste foundry sand, and further, it increases. In some cases, the used foundry sand content in the concrete increases the chloride permeability. Aggarwal and Siddique [61] stated that the concrete samples passed charges of 578, 628, 616, 600, 664, 652, and 741 coulombs for 0, 10, 20, 30, 40, 50, and 60% replacement of fine aggregates with waste foundry sand, respectively. As per ASTM C 1202- 19 [60], all the above samples have very low permeability as the charges passed were between 100 and 1000 coulombs. A graphical representation of the charges passed through the samples on rapid chloride permeability test (RCPT) at 56 days conducted by Hossain and Anwar [39] on lightweight concrete samples made with waste foundry sand and volcanic ash is shown in **Figure 10**.

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**Figure 11.**

*Sorptivity vs. % waste foundry sand.*

*A Review on the Usage of Recycled Sand in the Construction Industry*

The sorptivity of the concrete is due to the capillary rise of water from the bottom of the concrete specimen. Some researchers reported a decrease in sorptivity up to certain percentage content of used foundry sand and an increase in sorptivity after that. Bhardwaj and Kumar [40] reported that the sorptivity of geopolymer concrete made with waste foundry sand tends to decrease from 0 to 60% substitution of fine aggregate with waste foundry sand, and further addition of waste foundry sand in the mix increased the sorptivity. It is also observed that for the concrete having up to 80% of waste foundry sand, the initial rate of absorption (IRA) is less than the IRA of the control mix. Khatib et al. [62] reported that for the concrete made with natural sand replaced with used foundry sand at 0, 30, 60, and 100%, waste foundry sand (WFS) exhibited a consecutive increase in water absorption by capillary action when the WFS content increased in the concrete mix. A graph of the sorptivity variation of geopolymer concrete made with waste foundry sand as per Bhardwaj and Kumar [40] is shown in **Figure 11**.

Carbonation is the reaction of carbon dioxide in the atmosphere with the calcium hydroxide in the cement paste. This reaction produces calcium carbonate and lowers the pH to a value of around 9. The carbonation affects the durability of the concrete. Generally, the used foundry sand content in the concrete mix increases the carbonation depth. Prabhu et al. [15] reported that the carbonation depth on 180 days of the concrete made with used foundry sand increased with the percentage increase in used foundry sand in the concrete mix. At 365 days also, the carbonation depth observed was increasing with the percentage increase in used foundry sand. Siddique et al. [63] stated that the carbonation depth of concrete made with 0, 10, 20, 30, 40, and 50% used foundry sand at 90 and 365 days increased with the used foundry sand content in the mix. The carbonation depth variation at 180th and 365th days as per Prabhu et al. [15] for 25 MPa characteristic compressive strength concrete made with used foundry sand is

*DOI: http://dx.doi.org/10.5772/intechopen.92790*

**7.3 Sorptivity**

**7.4 Carbonation**

shown in **Figure 12**.

**Figure 10.** *Chloride penetration of lightweight foundry sand concrete.*

*A Review on the Usage of Recycled Sand in the Construction Industry DOI: http://dx.doi.org/10.5772/intechopen.92790*
