EXPERIMENTAL PROGRAM
Materials
1. Asphalt Cement grade 60/70 (AC 60/70)
2. Natural rubber in form of concentrated latex with high ammonia (HA)
3. Limestone that has properties and gradation
Preparation of Blends
1. Preparation of Natural Rubber Asphalt (NRA) started from heating asphalt cement with hot
2. When rubber latex was added into hot asphalt cement directly, foaming and frothing occur uncontrollably.
3. Stirring should be continued about 20 – 30 minutes after addition of rubber latex and maintain the temperature level in stability for homogeneity of the NRA binders
Mixing high content of concentrated latex would result in the NRA binder becoming more viscous and less homogeneous. From the morphology, it can see that the particle of rubber that spreads in the NRA binder became larger and rougher. Therefore, when it mixed with high content of concentrated latex, it needs to increase the mixing temperature so the NRA binder is liquidated enough to provide homogeneity. This also allows the NRA binder to have viscosity close to that of the asphalt concrete mixing process between asphalt materials and aggregates
Since mixing process utilizes high temperature with prolonged period of heating, the quality of NRA binders may decrease. Therefore, at the beginning of mixing process, it should be avoid to heat asphalt cement higher since temperature higher than this point can cause degradation for natural rubber
In addition to some suggestions regarding the preparation and storage of the NRA binders is also important. If we store the NRA binders at high temperature, they will degrade rapidly. Thus, time and temperature for storage of the NRA binders should follow allowable storage times The NRA binders needed to be slightly stirred before use to prevent binder segregation
Table 1. Allowable Storage Times for Natural
From the study of engineering properties of asphalt cement that mixed with natural rubber in form of concentrated latex in various proportions to be Natural Rubber Asphalt (NRA), these materials will be compared with AC 60/70. It can conclude the results in this research as
follows:
Binders
When asphalt cement mixed with concentrated latex at high temperature, particles of natural rubber will swell and will be absorbed by oily constituents of asphalt. Since natural rubber is a polymer compound that has a high molecular weight and it has a lot of complex molecular chain that it was caused polymer chain. These interactions help in the spread of natural rubber into asphalt cement, which make the binders more viscous and more elastic. Changes in properties of asphalt cement are as following:
An increase in viscosity helps asphalt cement to coat aggregates by thicker film. Such thicker film helps increase cohesion between aggregates that it reduces stripping for the mixtures. In addition, more viscosity helps increase softening point of asphalt cement
Concentrated latex could help increase elasticity of asphalt cement at low temperature. In addition, torsional recovery test which is a test for elasticity of asphalt cement showed that NRA binders provided higher percentage of torsional recovery than AC 60/70.
NRA binders could help reduce temperature susceptibility as penetration index (PI) increases by the amount of concentrated latex added.
An important characteristic when mixing asphalt cement with concentrated latex is that it helps increase elasticity and stiffness of asphalt cement at high temperature to prevent rutting according to the content of concentrated latex added. In addition, it helps asphalt materials flexible enough to prevent the pavement cracking from being stiff at low temperature.
Asphalt Concrete Mixtures
Asphalt concrete that were mixed with NRA binders could help increase density and stability while such mixtures require less optimum binder content than asphalt concrete mixtures that were mixed with AC 60/70.
In terms of performance properties, adding concentrated latex help reduce stripping of aggregates in asphalt concrete mixtures and increase resilient modulus at high temperature. Moreover, NRA mixtures also enhance fatigue and permanent deformation resistances better than conventional asphalt cement mixture. Compacting asphalt concrete mixtures is also an important issue since the mixtures have more viscous. The relationship between viscosity and temperature in different proportion of binders it can be used as guideline in mixing and compacting the asphalt concrete mixtures.
From the test results for engineering properties of asphalt cement mixed with concentrated latex or NRA, we found that it is suitable to use natural rubber in form of concentrated latex as additives in asphalt material for roadwork. This is due to superior engineering properties than AC 60/70 in all respects. More importantly, an increase in domestic consumption of natural rubber would prevent the decreasing of natural rubber prices and solve the problem of over capacity of domestic natural rubber in long term.
Although some engineering properties tend to be better by the content of concentrated latex added, it needs to consider some difficulties in preparing mixtures, mixing temperature, mixtures homogeneity, the increased viscosity, and workability. By considering under the laboratory tests for engineering properties of both binders and asphalt concrete mixtures Concentrated latex was the suggested appropriate proportion in blending with asphalt cement. approximately three times better than AC 60/70. Moreover, it requires less optimum binder content than AC 60/70 which may helps in reducing construction capital and long-term maintenance cost for road pavement.