**3.2 Effect of crude oil on the compressive strength of mortar and concrete**

The effect of different percentages of light crude oil (0, 0.5, 1, 2, 4, 6, 8, 10, 15, and 20%) on the mechanical properties of mortar and concrete was investigated. A comparison between the compressive strength of cement mortar and concrete with different levels of light oil contamination is presented in **Figure 5**. In this figure, the percentage (%) increase or decrease in the compressive strength was calculated, based on the strength of the uncontaminated samples (0%). It is worth noting that the overall trend was similar with a higher value of the compressive strength, as obtained in mortar compared to concrete. This is despite the total volume of light crude oil being less for concrete than for cement mortar, due to the addition of coarse aggregates, even though the mix percentage of oil contamination by weight of sand is the same. At 1% of crude oil contamination, the cement mortar exhibited a 24.4% higher compressive strength than uncontaminated samples, while only an increase of 7.49% was shown by the concrete. At 2% of crude oil contamination, the mortar

*Oil Contaminated Sand: Sources, Properties, Remediation, and Engineering Applications DOI: http://dx.doi.org/10.5772/intechopen.103802*

**Figure 5.** *Normalised compressive strength between mortar and concrete containing light crude oil contamination.*

still has a 10.5% higher compressive strength than uncontaminated samples, but the compressive strength of concrete decreased by 10%. Up to 9 and 17% lower compressive strength was observed for mortar with 6 and 10% light crude oil contamination, respectively, whereas the decrease in concrete was as much as 25 and 43%, respectively. At 20% light crude oil contamination, the reduction of compressive strength was almost the same for both mortar and concrete, which was around 80%.

The higher reduction in compressive strength of the concrete with oil contamination, compared to cement mortar, was due to two main reasons: (1) lower cement binder to aggregates ratio (C: A); and (2) bigger aggregate size. Decreasing the amount of binder reduces the ability of the cement to fully cover the aggregates, hence yielding a void structure that forms a path for water permeation. It can be noted that the total volume of the fine sand used with cement mortar was around 75% (1:3), while the combination of fine and coarse aggregates for concrete accounted for almost 85% (1:3:3). This can be related to the internal structure of a pervious concrete, which is relatively less compact due to the insufficient amount of binders which produce the voids [47]. In addition, the presence of crude oil in high percentages hinders the bond formation between the cement to the large surface area of the coarse aggregates, resulting in more segregation in concrete than in mortar [48]. As a result, the compressive strength was lower for concrete compared to mortar. Furthermore, as the aggregate size increased, the water permeability of concrete increased. It is worth mentioning here that the connected porosity increased as the aggregate size increased. Previous studies conducted by Fu et al. [47], Chang et al. [49] showed that the compressive and splitting tensile strengths increased as the amount of binder increased, and they decreased with an increase in aggregate size.

The higher strength exhibited by the cement mortar than the concrete, under different percentages of crude oil content, may also be due to an increase in the contaminated surface area of the aggregates. In the concrete mix, the surface area of the

**Figure 6.** *Surface area of the coarse aggregate under different crude oil contaminations.*

**Figure 7.** *Normalised relationships between the tensile compressive strength with different crude oil contaminations.*

coarse aggregate is also coated by crude oil, as shown in **Figure 6**, especially at a high level of crude oil content of 10 and 20%. As a consequence, the total surface area of aggregate achieved damp or wet status (saturation status). Achieving the saturation status of aggregate by crude oil means extra free water will remain in the mix. This hindered the bond formation between cement and the coarse aggregates, resulting in more segregation for concrete than for mortar [48]. As a result, the compressive strength was lower for concrete compared to mortar.

#### **3.3 Compressive and tensile strength relationship**

**Figure 7** shows the normalised effect on the compressive strength and splitting tensile strength of concrete containing fine sand with oil contamination. The behaviour of the splitting tensile strength shows a similar pattern to that of compressive

*Oil Contaminated Sand: Sources, Properties, Remediation, and Engineering Applications DOI: http://dx.doi.org/10.5772/intechopen.103802*

strength, but with the percentage of reduction less than for compressive strength. Jasim [50] have attributed this behaviour to the inconsistency of the effect of crude oil contamination between the tensile and compressive properties. Kovler [51] has indicated that adding some waste materials, such as superabsorbent polymers (SAP), to concrete can improve the tensile strength to a higher extent than the compressive strength. This can be related to the fact that tensile strength is sensitive to cracking, so any improvement of cracking resistance is expected to be beneficial in terms of tensile properties. This indicates that the viscosity of oil had a significant effect on the splitting tensile strength of concrete, compared to its compressive strength.
