Rubber concrete compressive strength

Polymer concrete samples of four compositions (Table 1.2) measuring 4 x 4 x 16 cm are prepared. Control samples were placed in a desiccator containing moisture absorption silica gel composition. Other samples were in environments with various humidity. The influence of environmental humidity on the compressive strength, modulus elasticity, and moisture absorption of furfurol-acetone, epoxy, polyester, and rubber (RubCon) polymer concrete samples are shown in Tables 1.3-1.5 and Figures 1.4 and 1.5. 

The ultimate compressive strength of the RubCon samples is 94.8 MPa. It is shown in Figure 1.9 that the strength of the concrete samples decreases moderately regardless of the environment s humidity. After a 50-day exposure, the strength limit stabilizes and remains unchanged until the end of the test. This can be explained by low water absorption of the rubber polymer concrete, not exceeding 0.05%. 

FIGURE 1.9 Dependence of compressive strength of rubber polymer concrete (RubCon) samples on exposition time at humidity of environment 1 50%-60%, 2 85%-95%, 3 water immersion, (From Yu. Borisov, Yu. Potapov, O. Figovsky, and D. Beilin, Water Resistance of the Polymer ConcretesJ. Scientific Israel Advanced Technology 14, no. 3 (2012) 84-91. With permission.)... 

As rubber concrete has long-term strength that is distinct from zero and creep damped out at compression, it is necessary to enter element E representing an elastic molecular skeleton of a material into the rheological material circuit (Figure 2.43). 

Extensive studies have been conducted on the use of recycled tyre to modify concrete and mortars [4-6]. The literature about the use of tyre rubber particles in cement-based materials focuses on the use of tyre rubber as an aggregate in concrete and evaluates only the mechanical properties. Results have indicated that rubberized concrete mixtures show lower density, increased toughness and ductility, higher impact resistance, lower compressive and splitting tensile strength, and more efficient sound insulation. 

Xiao [11] characterised the role of crumb rubber as a distribution of mini-control/expansion joints within concrete. Recently, Zhu [12] did an extensive analysis of the air content increase due to the presence of crumb rubber in concrete and developed a method to mitigate such an increase for the purpose of bringing back the loss in compressive strength for rubber concrete. 

This on-site remixing method means that crumb rubber was added at least 30 minutes after water was added and setting was beginning. On the other hand, it is speculated that most rubber concrete specimens made in a laboratory environment as reported in various studies referred to previously would have rubber and other materials mixed almost at the same time. Though whether the two ways to make rubber concrete will make a difference remains unanswered, it was noticed in one case from the rubber shot-concrete project that, the compressive strength for the specimens made in the laboratory was much lower than that measured on samples made from the job site. 

Presence of rubber also makes concrete more ductile or giving . Figure 11.2 shows the force-time response (displacement control) for two compressive strength tests in which... 

Figure 11.2 Force-time response for the compression of two concrete cylinders. The cylinder without rubber has a higher compressive strength but lower failure strain and energy absorption. The cylinder with rubber shows an opposite trend. Such a trend has been extensively observed in other similar tests [11].

Is there any chemical reaction between rubber and concrete Or will rubber participate in hydration in any capacity It appears that it is inadequate to even try to answer this question. Yet, there have been a few cases observed in which the relationship of compressive strength versus time for rubber concrete does not follow the pattern of controlled concrete. 

There was some speculation about whether those 179 kg per cubic metre rubber concrete pads (Mix-6) might disintegrate in any minute since its compressive strength was very low (see Table 11 ) as discovered later. But in the end, those pads still did what concrete was supposed to do, and have held up well since, though, with a very different and somewhat revealing characteristic in comparison with controlled concrete. 

Besides the two cases given here, it has been consistently observed that rubber crumbs do bring air into concrete, though the quantification can be very difficult. This increase in air content may act as a major contribution to the loss of compressive strength. 

Following the logic given previously that the increase in air content is to be blamed for loss of compressive strength, the question is to how to reduce the air content induced by the presence of crumb rubber. One method has been used to try and answer this question, in which additional fine particles that were smaller than mesh 200, such as fly ash, dust collected from the asphalt plant and even gypsum powders were used. Here, additional means to use more than what is normally specified in controlled concrete design. 

At the low level of rubber, rubber concrete essentially functions like controlled concrete and it appears that one possible application is as a replacement for air entrained concrete. The results obtained from the test site in NAU indicate that, while it performs well in a cold climate, rubber concrete has the advantage of higher compressive strength than air entrained concrete. Also, while it has good ability to resist cracks, rubber concrete may be used as controlled concrete but with fewer or no expansion joints. 

For resource reutilization, scrap tires have been investigated for a long time as an additive to concrete to form Rubcrete for various applications and have shown promising results (55). However, the addition of rubber particles leads to a degradation of physical properties, in particular, the compressive strength of the concrete. 

El-Gammal and co-workers [49] investigated the density and compressive strength of concrete that contained waste tyre rubber at various levels. The waste rubber had been used to replace equivalent amounts of fine and coarse aggregate in the test mixes. The results showed that, although there was a significant reduction in the compressive strength of the rubber modified concrete, the products demonstrated a ductile, plastic mode of failure as opposed to the brittle failure common with standard concrete. 

The bulk modulus of rubber, which depends on the strength of the van der Waals forces between the molecules, is 2 GPa. Therefore, the compressive modulus of a rubber layer increases by a factor of a thousand as the shape factor increases from 0.2 (Fig. 4.3). The responses are not shown for S < 0.2 such tall, thin rubber blocks would buckle elastically (Appendix C, Section C. 1.4), rather than deforming uniformly. When laminated rubber springs are designed, Eqs (4.5) and (4.7) allow the independent manipulation of the shear and compressive stiffness. The physical size of the bearing will be determined by factors such as the load bearing ability of the abutting concrete material, or a limit on the allowable rubber shear strain to 7 < 0.5 and the compressive strain e < -0.1. 

A review of research on the performance of concrete containing GRT particles was recently published (Pacheco-Torgal et al., 2012). In particular, this review discussed the effect of GRT treatment, the size of GRT particles, and the replacement volume on the fresh and hardened properties of concrete. A workability of fresh concrete defining its flowability and the compressive and tensile strength, toughness, elastic modulus, thermal and sound properties, and durability of hardened concretes containing the tire rubber waste was also discussed. 

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