Raimondas Šadzevičius

COMPARISON OF CONCRETE COMPRESSIVE STRENGTH VALUES OBTAINED USING REBOUND HAMMER AND DRILLED CORE SPECIMENS

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. Keywords: Rebound hammer, concrete core strength, reinforced concrete hydraulic structures. Article DOI: http://doi.org/10.15544/RD.2015.011

The technical state of earth dams in Lithuania

AbstractDams are ageing out as all constructions do, and inaccuracies during the field survey, designing and construction, as well as defects of building materials and deterioration due to environmental impacts accelerate the aging process. The article presents the technical state assessment comparable results of 260 Lithuanian earth dams performed in 2002–2009 and 368 dams in 1997; the analysis of character and causes of the main deteriorations and defects. The typical causes of failure (according to their danger to the stability of the entire hydroscheme) are: diverse intensity of seepage water leakage at the downstream slope and the tailwater of dam; landslides and deformation of the slopes of the dams; bigger cracks, deformation, tilt in shaft spillway; scour, deformation of dam slope protection slabs, concrete cover layer deterioration, collapsing of junctures are mainly caused by the environmental (frost cycles; ice, wave blows; moss, grass, bushes roots; periodical wetting, etc.) impacts.

Durability of Concrete Covering Layer of Reinforced Concrete Slabs for Earth Dam Slope Protection

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 freezing– thawing 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.

SUSTAINABLE CONSTRUCTION OF AGRO-INDUSTRIAL BUILDINGS FROM STRAW PANELS

Sustainable (environmentally friendly) modern construction is not limited only to use of natural and environmentally friendly materials. The concept of the construction is an important factor and that is applied to local materials, especially if they come from renewable sources. The sustainable (environmentally friendly) building principles, methods of construction from straw, the essential building requirements for construction from straw are discussed in the article. Straw as a building material used for a very long time, but this usage is often associated with certain mistrust, fears: the building will burn, the mice, rats are attacking, etc. Straw building uses raw materials which are agricultural waste. Buildings constructed from straw decompose in the end of their lifecycle and the construction waste in the area of construction is biodegradable, consequently, it is not necessary to take them away to a landfill. The evaluation of the global and Lithuanian experience of using straw and the structures in which straw are used shows, that the essential requirements can be provided if the straw and timber-framed buildings with straw as a heat insulating material are constructed properly, they use to meet the essential requirements according to the Law on Construction and the European Council and Parliament Regulation No 305/2011. Keywords: straw panels, agro-industrial buildings, sustainable construction. Article DOI: http://doi.org/10.15544/RD.2015.012

ESTIMATION OF TYPE AND AMOUNT OF AGGREGATES IN HARDENED CONCRETE

Sometimes happens that certificated concrete products, in which declarations of performance refer high strength and frost resistance indexes, start to deteriorate in first exploitation years. Due to aggressive environment this occurrence is frequent in concrete articles used for tiding surroundings: concrete paving blocks, slabs, curbs used for streets, parking places and pavements. Frequently, the main reason of deterioration is that concrete products are produced from the different concrete composition like samples, which have been used for certification. There are standard methods to estimate the amount of cement in concrete and to do a determination of air void characteristics in hardened concrete, but there are no methods how to estimate the amount and type of aggregates in concrete. For this reason, a new method was created. For the testing, the deteriorating paving zone, which had been built three years ago, was selected. The types of aggregates used in the production of concrete paving blocks have been estimated analyzing the cuts of the blocks. The test results show that the main aggregate, used for concrete paving block production, is gravel and it was used in higher amount as declared, while the granite breakstone and crushed gravel was used for production in lesser amount. In this case, the producer applying different amounts of aggregates reduced cost price as well as worsened the properties of concrete. Keywords: aggregates, concrete composition, early deterioration, paving blocks. Article DOI: http://doi.org/10.15544/RD.2015.009