Written by | Madiha Zaidi
Development of pavements reflects the rigidity in the planning and betterment of infrastructure in a town. The performance prediction model not only helps in generating information regarding behavior and life but also suggest life expectancy of the pavement. These models are the inputs of pavement management systems which helps in construction and rehabilitation of the pavement structure.
Bringing all this into an account, the idea of the project is to understand pavement material and examine the material behavior in pavement so that a performance prediction model is developed. The first step of the report covers the collection of current information regarding construction material in Karachi and the identification of various sources supplying aggregates to the construction industry. Construction sites, quarries and crushers in Karachi were visited to collect general information. It is evaluated that there is a dire need to develop a data bank which helps in identifying the most suitable aggregate for various construction purposes. To follow up this understanding a concept of aggregate characterization is presented.
The important part of the report is the aggregate characterization process in which very systematic approach is adopted to fulfill the demand of this idea. It is planned to conduct engineering tests and petrographic studies to evaluate the characteristic of the aggregate. The most initial stage is the collection of material which is divided in two parts that is from quarry and crusher of Hub river basin. This way sampling techniques are applied and material is collected and treated in respective testing program. The relation between the engineering behavior and petrographic studies is developed.
The distresses in asphalt pavement are identified by conducting field surveys on the main highways of Karachi. A GIS based imagery is developed which gives the idea of the distress severity on the entire road network.
The asphalt concrete samples were prepared using Hub river aggregate and wheel tracking testing is done at different temperature and asphalt content in order to evaluate rutting behavior. This task is performed to generate the results which were ultimately used in the development of the performance model.
This research presents the concepts, techniques and applications of aggregate characterization as a first step in the construction industry of Pakistan. The following are the conclusions drawn from the study:
1. It is found that color and surface condition projects the major variability in the rocks of Hub naddi and it should form the basis for sampling towards aggregate characterization.
All 7 conclusion
2. It has been found that Probabilistic and ANOVA approach for calculating sample size is suitable way to calculate the sample size for quarry and crusher respectively.
3. The aggregate of Hub Naddi consists of limestone and gives sound results for engineering and petrographic studies, that is, they yield a material quality acceptable for both HMA and concrete.
4. An aggregate resource map of Hub Naddi is now in hand in a developed form to be utilized as ready reference for the first hand knowledge of major quarries and crusher. This can act as a database to add on new sites and modify on existing ones as knowledge advances. The current study has set out a framework for exploring new sources/deposits and can provide results which would be highly beneficial to the construction industry of Pakistan.
5. Field distresses survey concluded that distresses are randomly distributed on the load lanes irrespective of the traffic loading that means other factors are also contributing in distress accumulation.
6. Based on the performance of Hot Mix Asphalt (HMA) carried under two control variables (namely temperature and asphalt content), it is concluded that at moderate temperature, rutting depend upon asphalt content, but at extreme temperature, it is not following any consistent pattern.
7. Regression modeling carried out for predicting rut depth at given temperature and asphalt content gives ±40% accurate results which are acceptable and presents an approach for pavement performance prediction modeling.
1. Development of a comprehensive database for the coarse and fine aggregate of Karachi which include the information regarding the source, crushing plant processing and properties in order to use the aggregates with respect to its suitability.
2. A GIS based imagery in the form of aggregate resource map should be developed which will identify all the source of aggregates in Pakistan and help in providing the information regarding the availability, quality and future demands of the material. It is recommended that the other quarries that were highlighted in the study and new quarries that must be explored; must be plotted on geo-referenced map so that can be utilized.
4. The other effecting factors like traffic loading, gradation, with water testing can be incorporated in the model so that a comprehensive rut model is prepared.
5. It is recommended to construct a petrographic study which is the instant way to classify the rocks on the basis of mineral content and gives the preliminary idea for the strength of rock.
6. The test to determine the percentage of fractured particles in coarse aggregate (ASTM D5821) as identified in literature review can also be included in the engineering tests list which is related to the performance of Hot mix asphalt.
7. A concerted effort has been carried out for the characterization of aggregates that will serve the construction industry by integrating all possible sources affecting their performance in concrete, HMA and other related construction materials. It is suggested that the current work for aggregate characterization would not only resolve the issue of regional resource planning, tempro-spatial dynamics of the are but would also possess the potential to resolve major construction issues related to material availability and suitability.