Материал: Russian Journal of Building Construction and Architecture

Russian journal of building construction and architecture

on the properties of materials, distribution gradients, intensity of solar radiation, wind, rain, external loads, etc. The simplex method is most effective (algorithm for optimizing linear programming by selecting the tops of cones in a multidimensional space). The method involves designing basic feasible solutions where the linear functional goes down monotonously until the necessary conditions of local optimality. This allows either to find an optimal solution or to establish that there is no one.

The essence of the simplex method is the following:

––to find out a method of identifying the optimal back-up solution;

––to establish how a transmission is made from one solution to another where the value of the objective function is closer to the optimal one, i.e. to find out how the back-up solution could be improved;

––to specify criteria that allows one either to cut short the selection of back-up solutions on the optimal oneorto concludethereis no one.

Operational properties that contribute to failure of the structure of asphalt concrete can be classed into three major groups:

––impact of transport on asphalt concrete of a road structure;

––impact of the environment causing degrading structural and mechanical characteristics of asphalt concrete;

––impact of the factors associated with the operation of asphalt concrete pavements.

As these factors are investigated further, there are new, previously unknown ones that influence the durability and reliability of asphalt concrete pavements. Depending on them, quantitative characteristics of life cycles of road pavements might change as well. An example of the calculation of thetime before a crack emergeson an asphalt concretepavement is shownin Fig.8.

The major method of improving the strength and durability of road structures is to increase the strength and stability of the subgrade as it is the msot vulnerable part of a structure [18]. Given the weather conditions of Vietnam, the following can be recommended to maintain and reinforce the subgrade embankment:

––when a level of ground waters has a significant effect on the humidity of the operating layer of the subgrade and in order to prevent the rainfall moisture from penetrating it out of the ruts and slopes, ditches should be drained;

––in order to prevent the rainfall moisture from penetrating the subgrade body through unattended ruts or waterproof ones, in order to prevent the rainfall moisture from penetrating a failing asphalt concrete pavement as well as to prevent the embankment subgrade from ditches in the periodof autumn groundwater,itis recommendedtousethe hydroisolation of the subgrade;

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–– for drainage of surface water and edge of the subgrade of long-term groundwater it is recommended to use ditches, back-up ditches by arranging slopes or designing terraces;

Structure of road pavement and its asphalt concrete

Bayley criterion

Fig. 8. Block scheme for calculating the time before a crack emerges on an asphalt concrete pavement using the simplex method

–– in areas with stable excessive rainfall moistening and where there is no surface drainage at a high groundwater level it is recommended that roadways are refurbished with the subbase is made of fine-grained materials – hydroisolation sublayer. Th is structure allows water coming through a pavement and ruts to be intercepted and the humidity of the operating layer of the subgrade to be decreased and its load-bearing capacity to be improved. All of the above are routine measures performed to reinforce and improve the quality of a

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Russian journal of building construction and architecture

pavement. They do not address the water and thermal balance of highways completely as do not account for particular conditions of an area, thus when applied for a specific road, it should consider local weather conditions.

Conclusions

1.An effect of atmospheric (humidity, temperature, solar radiation), hydrological (moistening of the subbase, changes in the soil temperature) and transport (dynamic impacts, vertical loading) factors contributingto the qualityof roadstructures of Vietnam can be classed into twotypes:

–– impact on the subgrade and pavement as a load-bearing structure resulting in changes in its strength, durability and performance;

–– impact on the pavement coating as a rolling surface resulting in changes in the state of its surface, rolling resistance, adhesion and thus a poorer “car-road” connection.

2.When choosing a technology for the maintenance and refurbishment of defects of subgrade and pavement, it is essential to cosnider the influence of a variety of weather and conditions that are Vietnam’s reality. It is only after the major cause of failure of road structures that a technology for the maintenance and refurbishment of road structures.

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