The use of asphalt is considered a key element for an effective road building process, contributing to economic savings as well as environmental protection for sustainable road construction
Main function of asphalt plant
An asphalt plant accurately doses the aggregates and asphalt cement to ensure the proportion established in the design and completely dry and heat the aggregates to obtain prefect adhesiveness with the asphalt binder. The plant also filters the gases from the combustion of the drying system and returns the fine aggregates to the mixer. It mixes the aggregates from the dryer and the fine aggregates from the bag filter with heated asphalt in the tank according to its viscosity and occasionally add additives to the mix while transporting it to a storage silo for subsequent unloading into the truck and transport to the road paver finisher.
One of the goals of asphalt concrete producers is to fabricate the asphalt mix with the same quality as the mix produced in laboratories, where the conditions are controlled and the production rate is much lower.
Cost
According to a study conducted by application engineers from Ciber along with some hot mix asphalt concrete producers in Brazil, more than 75 per cent of the total costs are related to direct materials such as aggregates and asphalt cement. The fuel used in the plant's dryer and for heating the asphalt in the tank are the third highest cost element, corresponding to almost 12 per cent.
The other costs include maintenance, freight and installation, infrastructure, electricity, wheel loader purchase and manpower, which represent less than 10 per cent of total costs. Ciber further showed that the investment in the asphalt plant has a less than 2 per cent impact on costs.
The preparation of the study was based on an annual mean production of 100,000 tonnes and repeatability for five years, under the same conditions. The cost of purchasing the inputs was according to the current situation in Brazil.
The maintenance costs were determined according to the cost of the wear parts and the wear time of these parts. Infrastructure costs included the price of a piece of land in a rural zone with the area needed to install the machinery and build the necessary infrastructure for the operation. Electricity costs were based on the estimated energy demand of the equipment and local price was set by the electric utility companies. The wheel loader is based on market price with interest and depreciation calculated under the same conditions established for the plant. Manpower was estimated according to need during the operation of the plant, management and administrative needs.
Opportunities for Savings in Asphalt Plants
The opportunities to reduce production costs are concentrated in the dosing and drying systems through accurate dosing of the aggregates and especially the asphalt, and in achieving perfect combustion and maximum heat exchange between the combustion gases and aggregates, resulting in lower fuel consumption.
Asphalt plants should have technologies to ensure accuracy in the dosing of materials. Marcelo Zubaran, application engineer and expert in products from Ciber Equipamentos Rodoviários, said, “Technologies currently applied in continuous plants, such as pick-up systems to read the real speed of the dosing belts and digital data transmission systems, ensure accuracy in the dosing of aggregates.”
“Since in continuous flow plants the dosage of the asphalt depends on the real weight of the aggregates, guaranteeing the accuracy of the aggregates dosage ensures accuracy in the asphalt dosage,” Zubaran added.
However, external factors such as correct measurement of the aggregates or contamination between silos can possibly lead to dosing errors. Zubaran explained, “If the plant regularly receives information on the humidity of the aggregates and if aggregates are not contaminated between silos, the mix will come out perfect, since the plant will certainly have done its part.”
The iNOVA 2000 plant model from Ciber aims to ensure a balanced heat exchange between the aggregates and combustion gases, which can reduce fuel consumption by up to one litre per tonne produced.
Investing in asphalt plants with more technology does not necessarily mean greater cost, since the return that such plants will deliver in terms of savings, production yield, final product quality and lower fuel, aggregate and asphalt costs, is higher than the difference in price for low technology plants.
