13-07-2012, 03:15 PM
USE OF TYRE RUBBER PARTICLES IN SLAG-MODIFIED
CEMENT MORTARS
USE OF TYRE RUBBER PARTICLES.pdf (Size: 672.68 KB / Downloads: 109)
ABSTRACT
Mortar specimens were prepared using slag-modified Portland cement and 10% (by weight of
mortar) of NaOH-treated rubber particles, smaller than 300 μm, from truck tyres (mainly SBR
rubber). Water sorption by capillarity and by immersion, resistance to acid attack, surface of
fracture analysis by scanning electron microscopy and flexural strength experiments were
performed. Flexural strength was reduced with the addition of the rubber (3.6 ± 0.5 MPa for the
specimens with rubber, 6.5 ± 0.8 MPa for the control). On the other hand, advantageous effects of
the addition of the rubber were observed on the transport properties of mortar. Sorptivity coefficient
was reduced from 0.29 (control) to 0.06 mm/min1/2. By immersion, the amount of water absorbed
by the specimens with rubber was reduced in 16 %. A significant decrease in the rate of weight loss
by acid attack was observed for specimens with rubber. SEM micrographs showed the presence of
microcracks in the specimens and closed pores in the specimens with rubber. These results show
that small rubber particles can improve some mortar properties even when used in a high
proportion.
1. INTRODUCTION
The ever-increasing volume of rubber waste in landfills from the disposal of used tyres has grown
into a serious environmental problem. Because rubber waste does not biodegrade readily, even after
long periods of landfill treatment, there is renewed interest in developing alternatives to disposal.
One possible solution for this problem is to incorporate rubber particles into cement-based
materials. Unfortunately, most research on using untreated tyre rubber in cement-based materials
shows that the degree of adhesion is poor, i.e., the rubber-cement interface is weak, leading to poor
mechanical properties. [1-7]
EXPERIMENTAL
Powdered tyre rubber, supplied by Borcol Industria de Borracha Ltda, Sorocaba-SP, Brazil, 50
mesh maximum size (300μm), was surface-treated with saturated NaOH aqueous solutions for 20-
30 min, at room temperature, under stirring. The mixture was filtered and the rubber was rinsed
with water until neutral pH and allowed to dry at room temperature.
Mortar test specimens were prepared with Brazilian slag-modified Portland cement (which contains
6 to 34% of blast-furnace slag), washed natural sand with 2.6 fineness modulus and water. The
mixture composition was water/cement ratio = 0.6, sand/cement ratio = 2. For specimens with
NaOH-treated rubber, 10% (by mass of mortar) was added to the mixture. The specimens were
cured for 28 days at room temperature (25°C) and 100% relative humidity.
RESULTS AND DISCUSSION
The failure of cement materials is governed by a process of microcracking, mainly associated with
the interfacial region between the cement and the aggregate particles. These internal cracks can
arise, for example, from processing defects such as pores. The uniaxial strength in compression is
commonly accepted as a general index of cement material strength. Nevertheless, the flexural test is
usually preferred for quality control of pavements, where the cement material is loaded in bending
rather than in axial tension.
Figure 1 shows the results of flexural strength for control and specimens containing NaOH-treated
rubber. A set of at least 46 specimens was tested in order to calculate the Weibull modulus, the
cumulative probability that a specimen fails during stressing in uniform tension (not shown in this
work). A reduction of c.a. 45% in flexural strength was observed for specimens with rubber.
CONCLUSIONS
Very few papers describe the properties of mortars with small rubber particles. In every case, only
mechanical properties are measured, which worsens [2,7]. We have shown that the addition of 10%
(by weight of mortar) of NaOH-treated tyre rubber particles in mortar reduced the sorptivity
significantly, and enhanced the resistance to acid attack, demonstrating the favorable effects of the
rubber on the transport properties despite the reduction in flexural strength observed in the
specimens.