Shrinkage Deformation Research Articles

Creep and shrinkage monitoring and modelling of CFST columns in a super high-rise under-construction building

Concrete-filled steel tube (CFST) giant columns have been widely used in super high-rise structures. However, there is a major shortage of field measurements of shrinkage and creep deformation from actual projects. Existing experimental results and derived models cannot reflect the actual on-site conditions where sustained loading is an incremental process during construction and the facing environments vary. In this study, the deformations of giant CFST columns in a super-high-rise under-construction building were monitored for more than 400 d. For comparison, a scaled experiment was conducted in a laboratory. The strains measured in the laboratory and on-site show a good changing trend over time and could be used for model verification. The existing CEB-FIP (2010) model is improved in two ways: 1) introducing a reduction factor in the calculation of shrinkage strains and 2) considering the stress history and stress redistribution in the calculation of creep strains. With parameters determined from the experimental results, the modified model could predict the shrinkage and creep strains of CFST columns in the actual project well with sufficient accuracy.

УПРАВЛІННЯ ПРОЦЕСАМИ СТРУКТУРОУТВОРЕННЯ ШЛАКОЛУЖНИХ ЦЕМЕНТІВ, АКТИВОВАНИХ СИЛІКАТАМИ НАТРІЮ

The article discusses approaches to the formation of the composition of slag-alkali cements when using high-modulus solution glass as an alkaline component, represented by a commercial product in the form of a liquid. The aim of this work was to study the effect of modifying additives, the silicate module of sodium hydrosilicates and technology modes on the processes of structure formation of artificial cement stone for effective control of setting time, intrinsic shrinkage deformations and achievement of high compressive strength (≥80 MPa at a standard age of 28 days and ≥ 20 MPa after 3 hours curing under normal conditions). As a result of the studies performed, a positive effect on the use of glycerin additives as part of a complex additive on the formation of the structure and properties of artificial stone was established. It is noted that the use of the studied modifying additives contributes to an increase in the degree of slag hydration, the formation, along with hydrosilicate compounds, of xerogel structures and celite-like compounds, which are deposited on the hydrosilicate-based matrix in the form of blocks-aggregates and increase the total volume of structure-forming compounds. A positive synergistic effect of using glycerin as an additional modifying component of the "trisodium phosphate + glycerin" complex additive for controlling the setting time in slag-alkali cements based on high-modulus solution glasses has been established. This made it possible to extend the time for the start of setting of slag-alkali cements when using solution high-modulus glasses from 3…5 min. up to values 26…83 min. Received cements with compressive strength after 3 hours 16.7...23.1 MPa, after 1 day 34.1...38.2 MPa, after 28 days 86.2...117.1 MPa with acceptable terms start of grasping. The heat release of such cements after 72 hours, despite their high activity, is only 150...180 J/h, which is 1.7...2 times less than that of fast-hardening Portland cement grade 600 and 2...2.4 alumina cement. Intrinsic shrinkage strains of compositions with modifying additives at the moment of stabilization were equal to 0.5…0.6 mm/m.

Direct electric curing in high early-strength sodium citrate-doped Portland cement systems for sustainable energy saving applications

Faced with the increasingly severe energy crisis, it is very important to seek a low-energy-consumption accelerated curing method for prefabricated concrete element to save energy in the construction industry. In this research, direct electric curing (DEC) was used to produce high early-strength cement sample, and sodium citrate was used to improve the durability of the paste. Meanwhile, the effects of DEC and traditional accelerated curing methods on the early-age strength of paste and the corresponding energy consumption were compared and discussed. The results indicate that the DEC makes the early-age strength of cement paste higher than that of steam-cured sample, but its energy consumption is only 4% of that of steam curing. Although DEC increases the early-ages strength of the cement sample without reducing its long-term strength, it increases the water absorption and drying shrinkage deformation of the sample. Meanwhile, incorporating sodium citrate to the electric-cured paste can effectively improve its durability by refining the pore structure. The reduction in energy consumption also means a reduction in production costs and carbon emissions. This means that DEC can replace traditional accelerated maintenance methods and improve production & energy efficiency, which may bring a technological change to the modern construction industry.

Effect of sulfoaluminate expansive additive on mechanical properties, internal relative humidity, and shrinkage of early-age mortar

Incorporating a suitable amount of sulfoaluminate expansive additive (SEA) into cementitious materials can compensate the shrinkage deformation. However, the influence of SEA on the relative humidity inside cementitious materials is still unclear. This study conducted a series of tests to investigate the mechanical properties, internal relative humidity, and shrinkage of early-age cement mortars containing different contents of SEA. Then finite element simulations of the drying of cement mortars with different contents of SEA were conducted to derive the moisture diffusion coefficient. The results reveal that the amount of expansive ettringite generated in cement mortar tends to increase with increasing SEA content, which can decrease the porosity of cement mortar and refine its pore structures. Both the compressive strength and flexural strength of cement mortar decrease with increasing SEA content. The decrease in mortar strengths is more significant during the later age. The mortar shrinkage under both sealed and drying conditions decreases with increasing SEA content. However, the compensation effect of SEA on the shrinkage deformation is less effective under drying condition. The relative humidity inside the cement mortar under sealed condition would decrease by 9.3% at 36 days when 8% SEA was used. While the decrease would be 3.4∼7.2% when the cement mortar was exposed to drying condition with RH of 60%. Moreover, since SEA densifies the microstructures and refines the pores in mortar, the moisture diffusion coefficient of mortar decreases with increasing SEA content.

Micro-nano bubble water process: Effect of micro-nano bubble water as mixing water on volume stability of shotcrete

As a kind of active water, micro-nano bubble water (MBW) can promote the early hydration of cement paste and improve the early mechanical strength of shotcrete. However, accelerating the hydration process of cement-based materials will increase their shrinkage deformation to a certain extent at early age. Therefore, this paper mainly studies the effect of MBW combined with aluminum sulfate alkali-free accelerator (AL) on the volume stability of cement-based materials within 180d. The results show that MBW as mixing water can reduce the autogenous and drying shrinkage of cement-based materials with AL, and also has a certain mitigation effect on water loss rate and internal humidity (IH) drop under dry conditions. It can also reduce the ring constraint shrinkage cracking time and crack width. MBW can reduce the cement paste pore size distribution of 10–50 nm, and reduce the surface tension of the aqueous solution, thereby reducing the capillary tensile stress. This paper provides some theoretical guidance for micro-nano bubble water in practical engineering applications.

Laboratory modeling of thermal and temporal cracking in swelling clays

Crack development in a changing environment is the controlling factor for the stability and strength of expansive soils. Expansive soils exhibit large volumetric changes with changes in their moisture conditions that may occasionally lead to reduced bearing capacity and foundation failures. This study purports to model crack initiation and its spatial progression in relation to the moisture content and drying period, respectively. Volumetric soil shrinkage is determined using high-definition digital camera imaging and Vernier scale methods, while the soil settlement under vertical shrinkage deformation could be captured through a tensile stress model for soils. It was revealed that a small change in suction could trigger crack initiation, which would propagate further under different environmental conditions. Furthermore, it was observed that the crack volume increased rapidly at specific moisture content and could penetrate as deep as 1 m after nearly 1.5 months that is fully consistent with the current model predictions. A comparison between the performance of the model proposed in this study and that of two existing models shows that the former predicts the vertical shrinkage strain values in closer agreement with those observed experimentally and is less conservative than those predicted by both models. Nevertheless, the findings from this study could be used to quantify the detrimental behavior of expansive soil present in pavement subgrades and shallow foundations for lightweight structures.

74‐1: Invited Paper: Highly Stretchable and Shrinkable AMOLED for Free Deformation

Flexible display technology has been successfully commercialized with foldable and rollable displays. Because of the limitation of the flexible technology, stretchable displays have attracted great attention which capable of realizing freeform design as a post‐flexible display. However, no technology has yet provided sufficient stretchability and resolution to realize genuine free‐form displays. We report on a highly deformable AMOLED display which capable of elongation over 20%. Moreover, our display is capable of more than 15% shrinkage deformation. We also developed low‐temperature thermal shrink process to make the most of the potential of the display. The fabricated full‐color stretchable AMOLED shows excellent deformability with high pixel density.

Effect of Curing Conditions on the Hydration of MgO in Cement Paste Mixed with MgO Expansive Agent.

Using the volume expansion generated by the hydration of the MgO expansive agent to compensate for the shrinkage deformation of concrete is considered to be an effective measure to prevent concrete shrinkage and cracking. Existing studies have mainly focused on the effect of the MgO expansive agent on the deformation of concrete under constant temperature conditions, but mass concrete in practical engineering experiences a temperature change process. Obviously, the experience obtained under constant temperature conditions makes it difficult to accurately guide the selection of the MgO expansive agent under actual engineering conditions. Based on the C50 concrete project, this paper mainly investigates the effect of curing conditions on the hydration of MgO in cement paste under actual variable temperature conditions by simulating the actual temperature change course of C50 concrete so as to provide a reference for the selection of the MgO expansive agent in engineering practice. The results show that temperature was the main factor affecting the hydration of MgO under variable temperature curing conditions, and the increase in the temperature could obviously promote the hydration of MgO in cement paste, while the change in the curing methods and cementitious system had an effect on the hydration of MgO, though this effect was not obvious.

Influence of whitening additives on the properties of decorative slag-alkali cements and mortars

The paper shows a comparative study of the influence of whitening additives (kaolin, TiO2 and СаСО3) on the production of decorative alkali-activated slag cement and mortars with a degree of whiteness of at least 70%; as well as their influence on the structure formation and evolution of physico-mechanical properties. According to results obtained, kaolin provides chemical bonding of Na+ into insoluble zeolite-like compounds; and CaCO3 densifies the structure and reduces shrinkage deformations. At the early stages of hardening (up to 7 days), the additions of kaolin and calcite, due to their significant amount (15 and 24%), reduces the compressive strength of the cement paste; nevertheless, at later ages (until 90 days) the difference in strength almost disappears. The high colourfastness and weather resistance of pigmented cements under the influence of ultraviolet radiation and freeze/thaw cycles has been established. A comparative assessment of the economic efficiency has shown that СаСО3 is the best cost-effective additive.

Chemical admixtures for concrete: Effects of accelerators on the volume stability of cement-based materials

In this study, the addition of sodium aluminate type alkali liquid accelerator (AR), aluminum sulfate type alkali-free liquid accelerator (AS), and fluoroaluminate type alkali-free liquid accelerator (AF) were used to test the volume stability, mass loss, and internal humidity change of cement mortar. The impact of various accelerators on the volume stability of cement mortar was examined through a comprehensive analysis utilizing MIP, XRD, IR, SEM, and other characterization techniques. The results show that the shrinkage deformation of the cement mortar mixed with AR type alkali accelerator was more serious than that of the mortar mixed with the other two alkali-free accelerators, and the shrinkage deformation of the cement mortar was more significant with the increase of the dosage of the three accelerators. The most significant reason for the shrinkage and deformation of the AR type alkali accelerator is that the conversion of AFt to AFm reduces the volume of swellable substances and the pore size distribution of 10–50 nm produces more significant capillary negative pressure. The reason for the smaller shrinkage deformation of the mortar mixed with two alkali-free accelerators is that its main component contains a certain amount of SO42-, and the undersulfated reaction will occur relatively less frequently. Furthermore, the 10–50 nm pore size distribution is less than mortar with AR type alkali accelerator, and the capillary negative pressure is lower. Additionally, quantitative analysis of the components was conducted to confirm the factors responsible for the varying levels of shrinkage deformation in the cement mortars with three accelerators.This paper offers valuable guidance for effectively employing accelerators in shotcrete applications.

Measurement of three-dimensional shrinkage deformations and volumes of stabilised soft clay during drying with Structure from Motion photogrammetry

The paper applies the Structure from Motion photogrammetry technique to measure three-dimensional shrinkage deformations of a cylindrical specimen during drying. A clay–binder mixture was statically compacted, and its shrinkage behaviour was observed for four weeks with a newly established photogrammetric system. The complete surface information including XYZ coordinates and RGB values was then reconstructed and formed into dense point cloud data, with which the volume change and shrinkage deformations are computed. In volume change determination, the reconstructed dense point cloud achieves a fine reproduction of the specimen surface, leading to satisfactory accuracy. The computed volume deviation was within 495.3 mm3 (0.24%) and 4170 mm3 (1.83%) for the dummy cylinder and clay specimen, respectively. Both values are significantly smaller than the volume deviations computed with a classical approach that involves artificially creating markers on the specimen surface. In the computation of shrinkage deformations, the paper proposes a novel method that detects the fast point feature histogram of the point clouds and then matches the detected descriptors, leading to an improvement in three-dimensional deformation determination. The compacted sample shrinks, and the computed axial deformations increase quasi-linearly with height. However, due to the noticeable tilt that occurred during drying, the calculated radial deformations are scattered at the same height and appear misleading. Circumferential deformations and strains are therefore adopted to represent the true material behaviour.

Construction and technical properties of vermiculite concrete and fibro vermiculite concrete with volcanic pumice under the influence of elevated temperatures

Objective. Development of compositions of vermiculite concrete and fibro vermiculite concrete with volcanic pumice. Investigation of the construction and technical properties of the developed compositions of vermiculite concrete and fibrovermiculite concrete with volcanic pumice under the influence of elevated temperatures.Method. Methods of increasing the fire resistance of reinforced concrete structures are considered. The research is aimed at the development of vermiculite concrete and fibro vermiculite concrete with volcanic pumice for fire protection of building structures and the manufacture of heat-resistant products and structures. To reduce the cost of vermiculite concrete, its partial replacement with volcanic pumice is proposed. For the study of vermiculite concrete with volcanic pumice reinforced with basalt fiber, a rotatable plan of the second order of the regular hexagon type was used.Result. Replacing a part of an expensive aggregate (expanded vermiculite) with pumice leads to a slight increase in the average density of the composite, while the bending and compressive strength increases. In addition, the heat-resistant properties of vermiculite concrete with pumice are increased. This is due to the fact that volcanic pumice, being a hydraulically active additive, is able to react hydration with cement components, eliminating the harmful effect of secondary hydration of free calcium oxide. The influence of the heating temperature on the change in the construction and technical properties of vermiculite concrete and fibrovermiculic concrete, including with the addition of pumice, has been studied. It was found that dispersed reinforcement with basalt fibers reduces shrinkage deformations, when heated to t = 800, the shrinkage decreases from 0.7 to 0.5% compared to the original concrete matrix.Conclusion. The dependence "compressive strength = f (average concrete density)" significantly depends on the presence and ratio of pumice in the composition of vermiculite concrete, while an increase in the holding temperature to 600 oC or 800 oC leads to a decrease in the compressive strength from 15 to 25%, and the main decrease occurs when heated to 600 oC, further the increase in temperature has a negligible effect. The dependence of the bending strength on the compressive strength is generally maintained regardless of the heating temperature, and the heating of concrete does not reduce the relative bending strength, i.e. the ratio of bending strength / compressive strength is not reduced. Dispersed fiber reinforcement increases the relative bending strength by about 70% regardless of the heating temperature.

Shrinkage and cracking sensibility of steel-alkali activated UHPC composite bridge decks

Alkali-activated ultra-high performance concrete (AAUHPC) is a concrete containing excellent properties such as high strength, high durability and low carbon emission. In this study, tests were carried out to investigate the basic mechanical properties of AAUHPC and restrained shrinkage behavior of steel-AAUHPC composite bridge decks. The effects of different parameters (e.g. the stiffness of steel deck, the thickness of AAUHPC layer, arrangement of studs and the temperature and humidity) on the early age contraction and cracking sensitivity of steel-AAUHPC composite bridge decks were investigated. The results showed that the AAUHPC deck without any internal or external restraint showed a higher shrinkage at a faster rate in the early stage. The rate of shrinkage in the later stage declined gradually with age, and the overall shrinkage deformation was found to be stable at the age of 28 days. For the reinforced AAUHPC composite decks subjected to internal and external constraints, the restrained effect of steel deck, studs and steel reinforcement on the shrinkage of AAUHPC was quite prominent which increased with the increase of steel deck stiffness and the thickness of AAUHPC, where as the temperature and humidity of environment showed a minor effect on the restrained shrinkage deformation at 28 days. The tensile properties and toughness of AAUHPC with steel fibers were found to be high. During the entire test, no cracks were observed on the surface of the reinforced AAUHPC composite bridge decks. However, the cracking risk of AAUHPC was high in the first 2 days, and the cracking risk coefficient in the later stage was about 0.2. In addition, the accuracy of the experimental results was verified by finite element analysis.

Effect of Mineral Admixtures on the Mechanical and Shrinkage Performance of MgO Concrete.

Shrinkage deformation of concrete has been one of the difficulties in the process of concrete performance research. Cracking of concrete caused by self-shrinkage and temperature-drop shrinkage has become a common problem in the concrete world, and cracking leads to a decrease in the durability of concrete and even a safety hazard. Mineral admixtures, such as fly ash and mineral powder, are widely used to improve the temperature drop shrinkage of mass concrete; fly ash can reduce the temperature rise of concrete while also reducing the self-shrinkage of concrete, there are different results on the effect of mineral powder on the self-shrinkage of concrete, but the admixture of fly ash will reduce the strength of concrete, and mineral admixtures have an inhibitory effect on the shrinkage compensation effect of MgO expander(MEA). The paper investigates the effect of mineral admixtures on the mechanical and deformation properties of C50 mass concrete with a MgO expander(MEA), aiming to determine the proportion of C50 mass concrete with good anti-cracking properties under working conditions. The experiments investigated the effect of fly ash admixture, mineral powder admixture and MgO expander admixture on the compressive strength and deformation of concrete under simulated working conditions of variable temperature and analyzed the effect of hydration of magnesite in MgO expander and pore structure of cement paste on deformation. The following main conclusions were obtained: 1. When the concrete compounded with mineral admixture was cured under variable temperature conditions, the compounded 30% fly ash and mineral powder decreased by 4.3%, 6.0% and 8.4% at 7d age, and the compounded 40% fly ash and mineral powder decreased by 3.4%, 2.8% and 2.3% at 7d age, respectively. The incorporation of MEA reduced the early compressive strength of concrete; when the total amount of compounding remained unchanged, the early compressive strength of concrete was gradually smaller as the proportion of compounding decreased. 2. The results of concrete deformation showed that when the temperature rose, the concrete expanded rapidly, and when the temperature dropped, the concrete also showed a certain shrinkage, and the deformation of concrete basically reached stability at 18d. 3. The compounding of 30% fly ash and mineral powder As the compounding ratio decreases, the deformation of concrete increases, and the 28d deformation of concrete with a compounding ratio of 2:1 is 280 × 10-6, while the final stable deformation of concrete with a compounding ratio of 2:1 in compounding 40% fly ash and mineral powder is the largest, with a maximum value of 230 × 10-6, respectively. Overall, the concrete with a total compounding of 30% and a compounding ratio of 2:1 has the best shrinkage resistance performance.

Spatiotemporal evolution of water and pore structure in cement-based material containing SRA by LF NMR

Shrinkage-reducing agents (SRA) have been extensively applied in cement-based materials for overcoming the shrinkage-induced cracks. The shrinkage behavior of cement-based materials is closely linked to evolution of water at different states and pore structure, meanwhile the shrinkage mechanism of SRA has not been clarified yet. In this study, the cement-based materials with different additions of SRA were prepared. The T2 relaxation spectra during the hydration and drying process were measured via low-field nuclear magnetic resonance (LF NMR), so as to explore the effects of SRA content on the water evolution and pore structure characteristics in cement-based materials. Meanwhile, the effects of SRA content on mechanical properties and drying-shrinkage deformation were analyzed by measuring the flexural strength, compressive strength and drying-shrinkage ratio. The results show that, the interlayer space (representative of T2 relaxation time) decreases, and then the water flows from gel pore to interlayer space during the hydration process. SRA can improve the contents of gel and adsorpted layer water and pore water. The increases became more obvious with the increase in SRA content, while the influencing degree of SRA weakened gradually as the curing age increased. Moreover, SRA significantly increased porosity and most probable pore diameter of cement-based materials, and the increases became particularly obvious at a larger addition. The shrinkage deformation of cement-based materials can be reduced after the addition of SRA. This is due to the fact that the addition of SRA lowered the evaporation of free water in cement mortar. So, the mortar maintained a high humidity in the hydration process, and simultaneously the pore size becomes thicker, causing the decline in shrinkage stress.

EVOLUTION AND DISTRIBUTION OF SHAKES IN LARCH LOGS DURING AIR DRYING

This paper analyzed the length, width, and location of shakes in the air-drying process of larch log (Larix principis-rupprechtii Mayr) 1 m long and 66% initial moisture content. The development law and distribution characteristics of shakes during log drying of larch were studied and shake generation and development law were analyzed from two aspects of microstructure and growth defects. The variation of dry shrinkage deformation along the radial direction and knot influence on it was analyzed using the split-shaped stress test strips. At the cellular level, the cell wall shrinkage behavior of heartwood and sapwood and the microstructure of knots were observed. The results showed a significant relationship between eccentricity and shake distribution; the IIa region is the most prone to dry shake. The evolution of shakes is closely related to the drying rate. In the high-speed drying stage (MC ≥ 40%), shakes almost do not occur; in the decelerating drying stage (40% ≥ MC ≥ 20%), the amount, length, and width of shakes increase rapidly. In the low-speed drying stage (20% ≥MC), the area of shakes tends to stabilize or even decline. The main reasons for dry shaking are the dry shrinkage difference between tangential and radial cell walls, early and late wood, heartwood and sapwood, and moisture content gradient during the drying process.

Research on welding deformation of hollow thin-walled complex structural parts based on plane bending theory of constant section beam

In order to effectively forecast the welding deformation and deformation pattern of hollow thin-walled aluminum alloy complicated structural parts, based on the plane deformation theory of constant section beam and workpiece constraint conditions, the complex feature structure was split and the deflection curve equation of each position was constructed. Moreover, the inherent strain method was used to solve the welding equivalent load, and the welding deformation was calculated by combining the equivalent load with the deflection curve equation. On the basis of the theoretical load value, the welding deformation at different positions during and after welding was numerically simulated by finite element simulation. What's more, the theoretical deformation of each plate is verified by the simulated deformation results. Besides, the simulation deformation results of post welding deformation are verified by welding experiment. The results show that the shrinkage deformation of the welding position is the largest, the transverse and longitudinal deformation are 0.007 mm and 0.018 mm respectively, the error rates of theory and simulation are 5.2 % and 5.5 % respectively. What's more, the welding deformation at the non-welding position is mainly reflected in the vertical direction of the upper skin plate. After the external constraints are released, the actual maximal deformation values of the two sides of the upper skin plate are 0.08 mm and 0.064 mm respectively. The deformation presents an M-shaped distribution, which is comparable to the deformation distributions of theory and simulation. The deformation value caused by the welding process accounts for 10 % of the total deformation after the removal of external constraints. In addition, the welding process is the main stage of forming the deformation distributions at each position, and the release of external constraints is the main factor leading to the final deformation.

Deformation Mechanisms of Magnesium Silicate Hydrate Cement with a Shrinkage-Reducing Admixture under Different Curing Conditions

Magnesium silicate hydrate (M-S-H) cement, a type of green building material, has poor volume stability (i.e., large shrinkage deformation), which limits its application. As a new type of admixture, the behavior of a shrinkage-reducing admixture (SRA) in M-S-H cement has not been studied. Therefore, in this research, the effect of SRA on the shrinkage properties of the M-S-H cement system was evaluated. The mechanism of SRA was investigated by surface tension measurement, hydration heat testing, thermogravimetric analysis, and pore structure analysis. Experimental results indicate that SRA can reduce the shrinkage of the M-S-H mortar, and the optimal effect is exerted when the dosage is 3.0%, drying shrinkage decreases by 22.6%, and autogenous shrinkage decreases by 60% on day 28. However, it may also adversely affect strength development. The presence of SRA in M-S-H cement can reduce pore solution surface tension, delay hydration, and maintain relative humidity within the slurry, which can be maintained at 82.0% on day 28. It can also increase pore size and porosity. The inhibitory effect of SRA on the shrinkage of M-S-H mortar is valuable for its future practical applications.

Effects of shrinkage reducing admixture and internal curing agent on shrinkage and creep of high performance concrete

The shrinkage and creep behavior of track beam concrete have the significant influence on the stability and safety of train operation. While superabsorbent polymer (SAP) and shrinkage reducing agent (SRA) are two commonly used admixtures in such high-performance concrete. So, the shrinkage and creep behavior of concrete with SRA or SAP were studied in this paper. Moreover, The microstructure of the interfacial transition zone (ITZ) observed by the scanning electron microscope (SEM) was discussed for the improvement of the mechanical properties of the concrete after the creep test. The experimental results indicate that SRA has a positive effect on reducing the shrinkage and creep deformation of concrete, and it is beneficial to the improvement of long-term strength and elastic modulus with little influence on creep recovery. In contrast, SAP reduces shrinkage, but increases the creep of concrete with less creep recovery and higher residual stress. Meanwhile, the fib 2010 model was revised to improve the ability to predict the creep of concrete containing SAP and other admixtures. Besides, it was found concrete after creep test has better mechanical properties, and the improvement of sample with SAP is the most obvious. The analyses of SEM also conformed that the concrete after creep test has a higher degree of hydration, and the denser ITZ microstructure.

RESEARCH OF DEFLECTIONS OF THE UNDERCRANE BEAM DURING THE OPERATION OF A BRIDGE CRANE USING THE METHOD OF LASER INTERFEROMETRY

Assessment of deformations and displacements of building structures is performed by solving many different problems. Depending on the specifics of the task, different measurement accuracy is required. In some displacement measurements, direct contact of the measuring device with some points of the structure under research is impossible: distant and high-placed structures, structures in the high temperature zone, etc. Contact with the measuring device of structures made of materials with low rigidity, thin films, elastic threads, or in cases where the material reaches the yield point is undesirable. In these cases, the inherent rigidity of the measuring device can distort the general picture of deformations, which will lead to significant errors. The article discusses modern methods of laser interferometry for non-contact assessment of movements and deformations of building structures, which make it possible to conduct unique non-contact measurements of both small and large deformations of various structures. The scientific value of the article lies in the fact that for the non-contact assessment of movements and deformations of building structures, it is proposed to use the most modern methods of laser interferometry, which make it possible to conduct unique non-contact measurements of both small and large deformations of various structures that work elastically, non-linearly, or are in plastic state in experimental conditions of high temperatures, radiation, with the provision of a high degree of automation of measurements and processing of results. The practical value of the research consists in the development of a technique that offers a non-contact assessment of movements and deformations of building structures using laser interferometry and makes it possible to provide measurements with an accuracy of 1×10-8 m and a frequency of 10-100 measurements per second with automation of registration and processing of results; carry out studies of building structures, buildings and structures in the mechanics of deformed solids and in the technique of surveying building structures, determining their performance, especially in conditions of high temperatures during fire resistance tests, in conditions of increased radiation, where high-precision and at the same time easy-to-use methods are required automated methods. The proposed technique provides unique opportunities for non-contact assessment of small deformations when studying the phenomena of shrinkage, swelling, creep, and plastic deformations. Keywords: deformations, measurements, interferometer, non-contact method, building structures.