Durability of reinforced concrete structures depends on the maintenance conditions, surveillance, and well-timed repair of structures or reconstructions. Usually, the main attention falls on the durability determination based on the evaluation of change of main physical -mechanical properties, especially, on the compression strength of concrete. In this study, tests with the rebound hammer and concrete cores extracted from the existing reinforced concrete elements in hydraulic structures are presented. The comparison of strength values obtained with the rebound hammer and the concrete core specimens of reinforced concrete in hydraulic structures is carried out. The research was performed during the scientific expedition in the period of 2010-2014. The investigated objects are allocated in hydroschemes of Druskininkai, Marijampolė, Klaipėda districts. It was established that the results obtained using the non-destructive method were by 17 % higher than the ones obtained by performing the destructive test. However, it can be said that despite this fact, the non-destructive method offers simplicity and rapidity in use: test results are readily available on site and there is a possibility to test concrete strength of those structures where cores cannot be drilled due to thin-walled or densely reinforced structures.

Cracks are classified according to their geometry (length, width and depth), statistical parameters (mean and variance of the number of cracks per unit area), crack riskiness for structures, etc. In this paper, crack openings in a reinforced concrete shell of the pressure piping at Kruonis Pumped Storage Power Plant, which appeared due to temperature change, are analysed. Detailed analysis of cracks and deformations due to temperature changes was performed after the evaluation of the technical state of the pipeline. Specific illustrations, calculations and guidance for repair of these deteriorations were offered.

Hydraulic structures are exploited in hard environmental conditions (impact of freeze-thaw cycling, ultraviolet, humidity and drying, acidity or salinity of water, abrasion etc.), so due to the impact of environmental factors some deteriorations will occur. The repeated cycles of freezing and thawing have significant effects on durability of concrete. They reducing durability, because of cracking and scaling of concrete. Using the research results of investigated hydraulic structures concrete average compression strength fck, water absorption by weight Wm, by formulae (1, 2) were calculated numbers of laboratory freeze-thaw cycles n50, freeze-thaw resistance of concrete rate F5 % and from themdurability indexprobable deterioration start time T5 % of investigated main hydraulic structures .( concrete strength fck loss in 5 % and 5 freeze-thaw cycles per year). Relationships between shaft spillway or retaining wall freeze-thaw resistance of concrete rate F5 % , durability index T5 % , and average compression strength of concrete fck were evaluated. These equations may be used for the durability prognosis of existing shaft spillways or retaining walls exploited in hydraulic structures.

Abstract. In Lithuania there are over 1000 ponds constructed and 620 have been evaluated as potentially dangerous hydraulic structures. Our water-retaining infrastructure deteriorates under environmental impacts, therefore the ageing of building materials causes a greater probability of deterioration and even failure. Durability of hydraulic structures depends on maintenance circumstances, surveillance, timely repair of structures or rehabilitations. Prognosis of the deterioration speed and durability of slabs is the main problem in each pond. The durability of concrete slabs covering layer can be evaluated by time (Tlayer), which equals the time to expose reinforcement of a reinforced concrete structure. Based on the results of the field investigation, the modelling of durability of reinforced concrete slabs for earth dam slope protection was performed. Regularities of concrete compression strength of reinforced concrete slabs for earth dam slope protection under the influence of freezingthawing cycles and other environmental factors were established. Using the developed durability evaluation method of reinforced concrete slabs for earth dam slope protection, the remaining service life of the construction till the probable beginning (T5 %) or end of its deterioration (T50 %) may be calculated. It is also possible to determine the time (Tlayer), during which the reinforcement of the reinforced concrete construction is uncovered/exposed. Using the estimated constant of degradation in designing of reinforced concrete slabs for earth dam slope protection for using them at changing water level, there is a possibility to choose concrete of such strength, that the reinforcement of the construction would not be exposed during the intended period of usage.

The cracks can be technological, appear during the usage time of construction, they can also be regular, and appear under the design load or they can also be unexpected and appear due to accidental impacts. Our research has shown that the cracks have appeared in reinforced concrete beams of the superstructure in quays No. 80 and 81 after the construction of Klaipeda Passenger and cargo terminal are caused by shrinkage strain, when the reinforced concrete beams has hardened. Normal hardening concrete shrinkage deformation is inevitable, but it depends on a number of factors, in particular, that in the present structures occurred because: - W/C ratio of concrete mixture exceeds the allowable values; - coarseness of selected aggregates (D = 16 mm) are too small for the construction of a massive wall; - concrete stratification and possible lack of care for hardening concrete (ambient temperature, etc.), this segregation could be affected by to big spread of concrete mixture (class of slump S3). The crack width at reinforced concrete beams in the superstructure of quay No.80 varies from 0.05 to 0.5 mm. This are a non-structural cracks, so they do not reduce significantly the mechanical strength and stability of the structure. Also, research has shown that the relationship between the crack width and the distance between the cracks is weak. Proposals for elimination of potential causes of cracking are presented according to the results.