The exploitation time and reliability of monolithic reinforced concrete structures largely depend on concreting technology and process influence during concreting and early setting stages. Different types of cracks in monolithic reinforced concrete structures appear due to internal and external effects. Cracks appear when the technology of structure concreting is damaged, when formwork is removed during the further setting and structures loaded period. In order to avoid micro and macro cracks in monolithic structures, it is important to measure the particular setting time moment and technological process moment when stresses that exceed the permissible values appear in concrete. The article analyses the processes that appear when horizontal, sloping and vertical monolithic reinforced concrete structures are concreted. The analysis of concrete mixture pressure on formwork is performed. The pressure which is calculated according to different countries’ methodology is different: the smallest pressure is obtained calculating according to the British recommendations, and the largest pressure is obtained according to French CIB recommendations. In Lithuania, it is recommended to follow the German DIN 18218 standard. The balance conditions of concrete mixture concreting on slope surface are described. The main concreting technology parameters and their interaction are analysed; the speed, intensity and time of continuous concreting technology are presented. When the process of continuous concreting is performed, it is necessary to evaluate the interaction and values of parameters properly. Methodical theoretical calculation is presented. Practical solutions for industrial building construction applying the modern sliding formwork technology are presented. The impact of cement type, superplasticizers and temperature over the concrete mixture mobility, changes, fresh concrete structural strength and concrete setting kinetics are analysed. The main characteristics of the initial setting — the beginning of structure formation, when concrete mixture turns into concrete state — is analysed applying the ultrasonic method. The beginning of structure formation influences the regulated time of concrete mixture laying and compaction. The requirements for structural strength (permissible strength limits) and concreting rate (formwork movement) of freshly formed concrete are set when the construction is performed applying the continuous concreting technology method. The analysis is implemented performing the construction of cylindrical sludge tank with slipping formwork. While performing the analysis during concreting, it was stated that the concrete setting kinetics corresponds to the sludge tank concreting rate. The analysis performed after concreting and in 28 days of hardening revealed that there are no surface defects or cracks, and concrete strength exceeds the required sludge tank design strength. Santrauka Monolitinių gelžbetoninių statinių konstrukcijų eksploatacijos trukmė ir patikimumas daugiausia priklauso nuo betonavimo technologijos ir procesų poveikių betonavimo bei pradinio kietėjimo metu. Straipsnyje nagrinėjami procesai, vykstantys betonuojant horizontaliąsias, nuožulniąsias ir vertikaliąsias monolitines gelžbetonines konstrukcijas. Atlikta betono mišinio slėgio į formas analizė. Tiriami pagrindiniai betonavimo technologijos parametrai, analizuojamas jų ryšys, pateikiamas nepertraukiamo betonavimo technologijos betonavimo greitis, intensyvumas, trukmė. Atlikti teoriniai skaičiavimai ir siūlomi praktiniai sprendimai pramoninių statinių statybai, naudojant šiuolaikinę slankiųjų klojinių technologiją. Ištirta cemento tipo, superplastiklių, temperatūros įtaka šviežiai suformuoto betono struktūriniam stipriui ir betono kietėjimo kinetikai. Nustatyti reikalavimai šviežiai suformuoto betono struktūriniam stipriui, betonavimo greičiui (klojinių kėlimui), vykdant statybą nepertraukiamos betonavimo technologijos metodu. Tyrimai pritaikyti vykdant cilindrinio dumblo pūdytuvo statybą slankiaisiais klojiniais.

No abstract

No abstract

The interaction between concrete and steel occurs during concrete mixing and finishing processes, during filling of concrete moulds, formwork, composite columns and during pumping of concrete mixtures. More experimental investigation is required to predict variations in interface friction, as a result of the composition of the lubrication layer which depends on the composition of concrete. This study provides experimental results to allow for a better understanding of friction at concrete-steel interface, with changes in the coarse aggregate (CA) content in the aggregate mixture (AM). Friction tests on fresh concrete have been carried out using the BTRHEOM tribometer (Nantes, France) and the interface parameters were calculated on the basis of the interface friction between the concrete and the steel wall, through the ADRHEO software. The roughness parameters were measured along the length of the rotary steel cylinder of the tribometer. In addition, the roughness of new and modified metal form-lining in steel composite columns was also measured. Variations in the CA content in the AM in the 42 to 52% range had minimal effects on the yield stress of the interface. The viscous constant of the interface as measured with a tribometer decreased, when the roughness parameter Rt values of the rotary cylinder wall, which refer to the absolute vertical distance between the maximum profile peak height and the maximum profile valley depth along the sampling length, were in the 17.10 to 28.73 μm range. The roughness profile peaks’ asperity recorded, was higher for the worn metal form-lining and for the steel composite columns with the inner surface covered in rust, when compared to the rotary cylinder roughness profile. The hypothesis is based on the principle that a sufficient lubrication layer, with the required thickness of fine mortar is created at the interface between the concrete and the metal form-lining or steel composite column wall, when the CA content in the AM varies in the range from 42 to 52% and the wall roughness parameters (Rt) of these elements varies in the 15.00 to 30.00 μm range.

The article discusses the technological peculiarities of construction monolithic hydrotechnical concrete structures, use of local aggregates for producing special concretes, methods of determining water impermeability of concretes as well as the evaluation of the methods mentioned above. The article presents the requirements for the granulometric composition of aggregate mixes for the production of flowing concrete mixes used for the construction of monolithic hydrotechnical structures. The possibilities and expediency of using local crushed gravel with increased amounts of weak particles for hydrotechnical structures are discussed. The mass loss of weak particles is slight compared with the whole mass of aggregates, and the total mass loss of crushed gravel it occurs due to micro-cracks present in particles. The frost resistance mark of crushed gravel and its suitability for hydrotechnical concretes should be determined by evaluating the amount of weak particles and their frost resistance. The article discusses concrete impermeability data received by means of two methods (according to LSTST 1974:2005 and LSTST EN 12390–8 requirements). Theoretical water penetration depths have been calculated. Determination of water impermeability according to LSTST 1974:2005 is recommended for C25/30 and lower compressive strength class concretes with W≤8. The LSTST EN 12390–8 water impermeability determina-tion method is recommended for C25/30 and higher compressive strength class concretes whose water impermea-bility mark is W≥8. For the construction of certain hydrotechnical structures water impermeable concretes whose water penetration depth should not exceed 20mm are recommended for use instead of the W6 and W8 concretes. Technological peculiarities and potential technological-organizational solutions for high walls of a water treatment plant have been discussed. The analysis of potential concreting methods of the reservoir’s high walls has been made as well as that of the key parameters of the continuous concreting process and their interaction. Dependences for the estimation of continuous concreting volumes and permissible concreted segment lengths have been proposed by evaluating the beginning of the intensive formation structure of concrete, number of layers in the height of the concreted wall and concreting intensity.