The aim of this research was the investigation of the properties of clay brick masonry arch bridge materials with a purpose of finding the best methods for reconstruction and renovation of the structure. The restoration, reconstruction and upgrading of historical heritage bridges require a careful investigation of materials and causes of damages. In many cases, the use of incorrect composition of joint mortar and clayed brick may lead to unfavourable result. It is important to ensure the natural water migration in historic masonry as it should not be interrupted after restoration or reconstruction measures performed. As an example the results of investigations and upgrading of historical clayed brick masonry bridge over the Venta River in Kuldiga town in Latvia had been analyzed. During the long lifetime and pro-active maintenance polity, the bridge had a lot of damages that could affect its further service life. For geometrical data collection laser scanning method was used that ensures sufficiently accurate data for reconstruction design, as well as the information for architectural investigation. Three-dimensional scanning of the heritage structure using 3D laser scanners allows the further transformation of information into the surface mesh model. This paper presents results of the investigation, and design of restoration and reconstruction works.

IntroductionMost of all bridges and by-passes in Riga are constructed after World War II and they are made from prefabricated reinforced concrete elements. Roads and bridges are treated with rock salt or salt solutions as a de-icing measure in frosty weather in the winter in Latvia. The amount of salt used for by-passes depends on the severity of the winter and varies from 6-7 kg/m 2 all season.In many buildings and reinforced constructions (bridges, by-passes, tunnels) everybody can see cracks, white or brown salt run off, carbonation of concrete and steel corrosion. To prevent these phenomena it is necessary to carry out investigations to solve the problems of corrosion, and conservation and restoration of concrete and reinforced concrete.As it is known deterioration of concrete dependence on many factors: aggressive substances, including water, which penetrate through the surface and accumulate in the outer concrete layer and penetrate further into the bulk of the concrete /1-4/.There are really three basic mechanisms to consider: 1. Physical deterioration, e. g., freeze thaw action including de-icing salts and the restraining effects of thermal gradients, cracking, abrasion and wear, or salt scaling due to recrystallization of salts in the pores where the expansion pressure of crystal growth leads to surface scaling of concrete and reducing the quality and strength. 2. Chemical deterioration, i. e. concrete reacting with the surrounding media causing either expansion of the concrete leading to cracking and spalling (alkali-silica reaction or sulphate attack) or dissolution and disintegration of the cement paste which binds the fine and coarse aggregates together. 3. Electro-chemical deterioration, i. e. corrosion of steel reiforcement having been depassivated either by carbonation or chloride contamination of the both /5-7/. In order to investigate the corrosion of concrete and reinforced constructions about forty samples of 3 Riga bridges were taken as cores from different places and analysed.As the most interesting object from corrosion aspect we chose the viaduct across Daugavgrivas street. The viaduct is an extension of Vanshu brigde accross the river Daugava and is located on the left side of the river.It is built in 1981 and is made from prefabricated reinforced concrete elements, the surface is overlaid with rolled asphalt. In this viaduct everybody can see all corrosion processes of reinforsed concrete.In fact the main reasons for deterioration of concrete in service life are water, salt solutions and change of temperature.For investigations of these processes samples of various substances were taken in different places:• water from pits in asphalt,