**6. Properties of hardened concrete made with used foundry sand**

Many researchers reported the hardened properties of concrete made with used foundry sand at different curing periods. The mechanical properties include compressive strength, split tensile strength, flexural strength, and modulus of elasticity. The mechanical properties of hardened concrete made using waste foundry sand are discussed in detail in the following paragraphs.

#### **6.1 Compressive strength**

The concrete incorporating used foundry sand generally shows higher compressive strength than the normal concrete. In some cases, the compressive strength of concrete made with partial replacement of fine aggregates with used foundry sand was below or equal to that of the control mix. Siddique et al. [54] reported that the concrete having the 28th-day compressive strength of 28.5 MPa made with 0, 10, 20, and 30% replacement of sand with used foundry sand, the compressive strength was consecutively increased from 28.5 to 31.3 MPa. Manoharan et al. [28] reported the 28th-day compressive strength of concrete with 0 and 20% chemically bonded

used foundry sand as 24.8 and 26.5 MPa, respectively, and for 25% used foundry sand, the compressive strength was below the compressive strength of control mix. In the majority of the research findings, the concrete containing used foundry sand has higher compressive strength than conventional concrete. As per Siddique et al. [54], the increase in compressive strength of the concrete made with used foundry sand may be due to the higher fineness of the used foundry sand than the regular sand, which resulted in the formulation of a denser concrete matrix along with the silica content present in the used foundry sand.

In some cases, the compressive strength of used foundry sand incorporated concrete is more or less the same as that of the control mix up to a certain percentage of used foundry sand content, and after that, the compressive strength decreases significantly. Prabhu et al. [53] stated that the concrete mix containing foundry sand up to 20% replacement of fine aggregate with foundry sand, the compressive strength observed was moderately close to the strength of the control mix, but beyond 20% replacement, the concrete mix showed lower strength than control mix. Some researchers pointed out specific reasons for the reduction of compressive strength of concrete made with used foundry sand beyond certain replacement levels of fine aggregate with used foundry sand. Singh and Siddique [31, 56] and Siddique et al. [57] pointed out that the compressive strength of concrete containing used foundry sand above a particular percentage gets reduced probably due to the increase in surface area of fine particles, which lead to the reduction of water-cement gel in the concrete matrix, and hence, the binding process of the coarse and fine aggregates does not take place properly. The graph of the compressive strength of ultra-high-strength concrete made with natural sand replaced by foundry sand at 0, 10, 20, and 30% at 7, 14, and 28 days as reported by Torres et al. [33] is shown in **Figure 6**.

### **6.2 Split tensile strength**

Depending on the source of used foundry sand, the concrete incorporating used foundry sand shows inferior or at par or superior split tensile strengths than the regular concrete.

In some cases, the split tensile strength of concrete made with used foundry sand increases with the percentage increase in used foundry sand in the concrete mix up to a certain level and decreases afterward. Sohail et al. [30] described that up to 40% replacement of river sand with waste foundry sand from a gray iron foundry, the split tensile strength of concrete at 28th day increases, and further, it reduces consistently up to 100% replacement. Patil et al. [58] confirmed that the split

**19**

**Figure 7.**

*Split tensile strength vs. % waste foundry sand.*

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

replacements as per Bhardwaj and Kumar [40] is shown in **Figure 7**.

The flexural strength of the concrete containing used foundry sand shows marginal variations with the addition of used foundry sand. The flexural strength of concrete incorporating used foundry sand usually increases marginally to that of normal concrete. In the research on the properties of concrete with used foundry

**6.3 Flexural strength**

tensile strength of concrete of 30 MPa characteristic compressive strength made with partial replacement of fine aggregates with waste foundry sand increases up to 10% replacement, and further, it decreases in which the control concrete has a split tensile strength of 3.30 MPa, whereas at 10% waste foundry sand content, the split tensile strength increased to 3.87 MPa. Siddique et al. [54] reported that for concrete of 28.5 MPa characteristic compressive strength, the splitting tensile strength was consistently increased from 2.75 to 3.00 MPa from 0 to 30% replacement of regular sand with used foundry sand. In some research findings, the tensile strength of concrete with used foundry sand was found decreasing as the used foundry sand content increases. Seshadri and Salim [12] observed that, for the high-performance concrete with partial replacement of fine aggregate with used foundry sand, the split tensile strength was decreased with the increase in the percentage of used foundry sand from 0 to 40%; at 0% used foundry, the concrete has a split tensile strength of 6.30 MPa, whereas at 40%, the split tensile strength of concrete reduced to 4.40 MPa. Prabhu et al. [53] reported that the split tensile strength of concrete containing foundry sand at 20% substitution of fine aggregate with used foundry sand showed almost equal splitting tensile strength as that of control mix, and the tensile strength in general marginally decreases with an increase in the percentage of foundry sand in the concrete mix. Bhardwaj and Kumar [40] reported that the split tensile strength of ambient cured geopolymer concrete of 40 MPa compressive strength at 28 days made with waste foundry sand increases up to 60% replacement of natural sand with waste foundry sand from the ferrous foundry and decreases afterward for further increase in waste foundry sand percentage. A graphical representation of the split tensile strength of geopolymer concrete of 40 MPa compressive strength at 28 days made of waste foundry sand at different percentage

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

**Figure 6.** *Compressive strength vs. % foundry sand.*

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

tensile strength of concrete of 30 MPa characteristic compressive strength made with partial replacement of fine aggregates with waste foundry sand increases up to 10% replacement, and further, it decreases in which the control concrete has a split tensile strength of 3.30 MPa, whereas at 10% waste foundry sand content, the split tensile strength increased to 3.87 MPa. Siddique et al. [54] reported that for concrete of 28.5 MPa characteristic compressive strength, the splitting tensile strength was consistently increased from 2.75 to 3.00 MPa from 0 to 30% replacement of regular sand with used foundry sand. In some research findings, the tensile strength of concrete with used foundry sand was found decreasing as the used foundry sand content increases. Seshadri and Salim [12] observed that, for the high-performance concrete with partial replacement of fine aggregate with used foundry sand, the split tensile strength was decreased with the increase in the percentage of used foundry sand from 0 to 40%; at 0% used foundry, the concrete has a split tensile strength of 6.30 MPa, whereas at 40%, the split tensile strength of concrete reduced to 4.40 MPa. Prabhu et al. [53] reported that the split tensile strength of concrete containing foundry sand at 20% substitution of fine aggregate with used foundry sand showed almost equal splitting tensile strength as that of control mix, and the tensile strength in general marginally decreases with an increase in the percentage of foundry sand in the concrete mix. Bhardwaj and Kumar [40] reported that the split tensile strength of ambient cured geopolymer concrete of 40 MPa compressive strength at 28 days made with waste foundry sand increases up to 60% replacement of natural sand with waste foundry sand from the ferrous foundry and decreases afterward for further increase in waste foundry sand percentage. A graphical representation of the split tensile strength of geopolymer concrete of 40 MPa compressive strength at 28 days made of waste foundry sand at different percentage replacements as per Bhardwaj and Kumar [40] is shown in **Figure 7**.
