Volume Changes Of Concrete Research Articles

The Effect of the Composition of a Concrete Mixture on Its Volume Changes.

The presented research aims to clarify the specific effect of the individual components of concrete with Portland cement CEM I 42.5 R on the volume changes of concrete. The effect of the filler component was evaluated from the point of view of the composition and type of aggregate (crushed versus mined) and from the point of view of the mineralogical composition of the aggregate. Concrete formulas with a maximum aggregate grain size of 16 and 22 mm were assessed. The effect of the binder component on the shrinkage of the concrete was monitored on the concrete mixtures produced using the same aggregate and maintaining the same strength class of concrete, C 45/55. The effect of the addition of finely ground limestone, finely ground granulated blast furnace slag and coal high-temperature fly ash was monitored. It was found that the maximum aggregate grain and the type of grading curve do not have a significant effect on the volume changes of concrete. Concretes with mined aggregates showed lower shrinkage than concretes with crushed aggregates. The most significant is the effect of the type of aggregate on the volume changes in the first 24 h. Mineral additives have a positive effect on the elimination of the volume changes of concrete, while the addition of high-temperature fly ash proved to be the most suitable.

CONCRETE STRUCTURES INTERACTING WITH SUBSOIL DEPENDING ON THE USE OF SLIDING JOINT

Article describes the interaction of concrete structure (usually foundation structure or industrialfloor) with subsoil, where unwanted friction occurs. Friction can be reduced with sliding joint. This generallyknown assumption is followed by research described in the article, which determines the effectiveness ofsliding joints with respect to concrete volume changes on large-dimensional specimens. Large-dimensionalspecimens with dimension of 150 x 500 x 6000 mm were placed in the laboratory and outdoor environment,defining different boundary conditions. The research included various concretes in the same strength class andvarious sliding joints that respect the requirements of construction practice. The paper also describes thecomparison of measured results with calculation models from technical standards and regulations, which allowcalculation of volume changes on concrete structures. Regarding the subsoil and the sliding joint, this is one ofthe main long-term goals of the research, since the calculation models do not take these two parameters intoaccount. Deformations from volume changes then deviate significantly from theoretical calculations, as frictionin the sliding joint area affects the magnitude and course of volume changes. Practical results show that thesteel fibres mixed into concrete have a positive effect on reducing volume changes in early stages of settingand hardening of concrete. Regarding the use of the sliding joint, the most important finding is that there areno significant differences from the selected sliding joints in the experimental part. In connection with friction,the use of the sliding joint itself has a significant effect.

The Impact of Different Aggregate Types and Its Composition on Resulting Concrete Properties Representing the Water Impermeability Level of Concrete for the Construction of White Boxes

We understand the term 'white box' as a concrete structure in underground spaces, basements, or cellars, where it is necessary to consider the water impermeability of concrete or minimal changes in volume changes of concrete. These properties can be attained by creating the maximal compactness of the concrete composite when using the optimal combination of entrance components. The goal of this article is mainly to verify the effects of aggregate variety and its granulometric curve during the observation of volume changes and the water impermeability of concrete and another property, which are in white boxes constructions important. Granulometric curves of aggregates will be designed to ensure the minimal voids content of an aggregate, and the effect of the discontinuous granulometric curve will also be observed with respect of this property. During the design of the concrete mixtures, account was taken of a high amount of binding agent, which is used ensuring the higher compactness of cement stone was considered besides. For this reason, it will be verified also additive of finely ground limestone, thanks to which it is possible to partially replace a part of cement while maintaining the same properties of concrete. This method of design can lead not only to positive elimination of volume changes in a concrete mixture but also has a significant impact on dried concrete parameters, such as a high level of water impermeability.

Early age concrete volume changes and thermal actions in practice of reinforced concrete liquid tanks design

Early age concrete volume changes and thermal actions in practice of reinforced concrete liquid tanks design

Experimental investigation of the influence of the plasticizing agent on the properties of cement mortars

Negative properties of concrete include the volume changes occurring during their solidification and hardening process. These deformations and cracks lead to reduce the strength and the durability of structures. The most important volume change of concrete is shrinkage resulting from the ongoing physical and chemical processes. The concrete with a high water to cement ratio is especially prone on the drying shrinkage. This article deals with the verification of the properties of cement mortars using selected kinds of plasticizing agents developed for self-levelling cement screeds. Applied agents (MS 3-12, MS 4-12, MS 5-12 and reference Berascreed 101) are based on modified polycarboxylates. The dosage of these agents was determined by the previous research in the amount of 1.5% by weight of the binder. The use of agents had a positive impact on the consistency of the fresh cement mortars and increased values of the initial and the long-term compressive strength. The negative impact of these agents was noted at the shrinkage and bulk densities of fresh and hardened cement mortars. Based on the achieved results can be concluded, that the plasticizing agent MS 4-12 may be considered a suitable substitute for the reference agent.

Experimental Measurement of Volume Changes on Cement Concrete Depending on the Subsoil

The paper describes experimental measurement of volume changes of cement concrete elements depending on the subsoil. Volume changes of cement concrete (including shrinkage and swelling) are theoretically known and at present there are many calculation models to determine the final shrinkage at the time of the design of the concrete or construction. The subsoil beneath the concrete structure has a significant effect on the volume changes of the concrete, and this behaviour must be considered when designing. However, the calculation models do not consider the influence of the subsoil and friction effects. The experiment described in the article includes the behaviour of different concretes on differently defined subsoils. At the defined input conditions, volume changes have been measured over the long term in different climatic conditions. The result of the experiment is the values of volume changes, depending on the concrete-subsoil interaction.

Effects of Polypropylene Fiber Content on Strength and Workability Properties of Concrete

Low tensile strength of plain concrete is due to the inherent presence of microcracks due to drying shrinkage occurrences or other causes of volume changes in concrete. The addition of a proper amount of fibers to concrete would act as crack arrester thus improves its static or dynamic properties. In this paper, the concrete with different amount of polypropylene fiber was investigating to find out the fibers effect on its fresh and mature properties. A plain concrete mix (reference mix) prepared for comparison purposes. Nine concrete mixes were prepared with different fiber volume fraction (FVF) ranging from 0.06% to 2.16%. It has been found out that the fiber content of the concrete mix will increase compressive, splitting, and flexural strengths of the concrete at the age of 28 days. The strengths increased and reached their maximum value at a corresponding (FVF) of about 0.36%. In comparison with the reference mix, the increase in the maximum compressive strength was about 18%, while the increase in maximum splitting tensile strength was about 16% and the increase in flexural strength was about 14%. When the fiber content increased beyond the mentioned 0.36% volume fraction: The concrete strengths started to decrease due to high volume fiber interface with the cohesiveness of the concrete matrix causing difficulty in concrete compaction with lowering its workability. At fiber (FVF) of 0.96%, the concrete slump value became zero. Thus, forced vibration needed for the compaction. For each mature concrete mix density and water absorption percentage were measured. It has been noticed that with an increase of fiber dosage in the concrete mix its density will decrease leading to contrarily an increase in the water absorption percentage. This was due to an increase in air void in the concrete due to the reduction in the workability of the concrete.

The assessment of Levenberg–Marquardt and Bayesian Framework training algorithm for prediction of concrete shrinkage by the artificial neural network

Shrinkage and creep are the main concrete volume changes over time. This unacceptable concrete deformation leads to stress and cracks creation where eventually reduces the service life of concrete structures. According to this, the prediction of shrinkage and creep strain in concrete structures with acceptable accuracy is the significance essential. The extensive investigation accomplished by several researchers has created different relationships and models for forecasting of shrinkage and creep strain based on experimental and analytical observation. Despite effective efforts in this regard, existing models do not have sufficient accuracy for anticipate of shrinkage strain. According to this, in this research, it has been attempted to provide a shrinkage predicting model based on the artificial neural network technique with the application of RILEM database. Also, it has been tried to determine the accuracy of the proposed model in comparison to the existing standard models by statistical analysis. According to the obtained results, by application of the neural network technique, the shrinkage strain could be predicted with acceptable accuracy especial in the extended period.

Parameter Analysis of the Reinforcement for the Width and Spacing Control of the Early-Age Cracks in Concrete

Early-age volume changes in concrete induced by temperature change, hydration, autogenous and drying shrinkage can lead to concrete cracking and this can have lasting effects on serviceability, durability or aesthetics of the structure. The restraint to thermal movement is the product of the coefficient of the temperature fall from a peak level during cement hydration and a restraint factor. In most cases it is not necessary and also not economical to avoid cracks. In these cases, crack widths are limited due to water tightness, durability or aesthetic reasons. If early-age thermal cracking cannot be prevented, crack width can be controlled with reinforcement. The reinforcement distributes cracks and consequently reduces their widths and spacing. As a result, there forms a large number of smaller cracks instead of a few through-cracks. This means, that due to the formation of fine cracks, the strain capacity of a reinforced concrete element before the occurrence of through cracks can be increased with the help of skin reinforcement. This paper discusses the parameters of reinforcement affecting the width and spacing of early-age cracks in concrete. The effect of reinforcement on early-age cracking in concrete was investigated on numerical simulation and in full-scale experiments. The test variables were the reinforcement ratio and the cover thickness of the longitudinal reinforcing bars.

Spalling related to Coefficient of Thermal Expansion (CoTE) of Continuously Reinforced Concrete Pavement in Texas

Concrete volume changes due to temperature and moisture variations (environmental loading) are severely restrained in Continuously Reinforced Concrete Pavement (CRCP) by longitudinal reinforcement and base friction, resulting in numerous transverse cracks, which are held tight by primarily longitudinal steel. Tight transverse cracks provide good load transfer at transverse cracks, ensuring good performance of CRCP. In general, an adequate amount of longitudinal steel and base friction used in CRCP will restrain concrete volume changes to an adequate level, keeping transverse cracks tight and providing good CRCP performance. In Texas, the performance of CRCP is excellent; however, severe spalling problems have been observed in CRCP sections where a certain type of coarse aggregate was used, resulting in costly repairs and traffic delays. This study investigated the causes of severe spalling problems in CRCP in Texas. Fourteen CRCP sections with severe spalling and 10 sections with no spalling distress were identified. A minimum of two cores were taken from each section and concrete material properties, including Coefficient of Thermal Expansion (CoTE) and modulus of elasticity, were evaluated. Test results indicate a strong correlation between spalling and concrete CoTE. Concrete with a CoTE larger than 9.9 × 10-6/°C (5.5 × 10-6/F) is quite prone to severe spalling. On the other hand, CRCP sections with a concrete CoTE smaller than 9.9 × 10-6/°C showed almost no spalling problems.

Modeling of volume changes of concrete mixed with expansive additives

This study modeled volume changes of concrete mixed with expansive additives, a countermeasure to shrinkage. Volume changes of expansive paste are determined from the balance between the shrinkage of cement and the expansion of the additives. Therefore, in this study, volume changes were modeled by applying a balance to the hydrates of cement and the expansive additives. The shrinkage of cement was modeled by assuming that it is caused by capillary tension. This modeling was based on the behavior of the moisture inside the cement’s pore structure, by taking into account the pore size distribution and the thermodynamic equilibrium state of the moisture. Using the concept of effective radius factor, the expansion of the expansive additives was modeled by considering the volume expansion of the additive particles caused by an increase in the outermost radius of particles of the hydration products that were formed at an early age. The values predicted by the model were consistent with the measured values, which confirms the model’s validity. Furthermore, the volume changes of concrete were estimated with sufficient accuracy by analyzing the behavior of the paste using a composite model of aggregate and paste.

Full-depth concrete pavement repair with steel reinforcements

Some of the conventional Full-Depth Repairs (FDR) in Jointed Concrete Pavement (JCP) suffered recurring failures in less than one year. Under very heavy truck trafficking, tie bars were ruptured, and the slabs were settled for as much as 100mm. This indicates the conventional method of slab replacement does not address the underlying problem. Falling Weight Deflectometer (FWD) and Dynamic Cone Penetrometer (DCP) were utilized to determine Load Transfer Efficiency (LTE) and base/subgrade support conditions, respectively. After one month of the heavy truck trafficking since opening to traffic, some transverse joints had LTE less than 10%. DCP results confirmed extremely weak base/subgrade support. It was concluded that the weak base/subgrade support was one of the main culprits for the recurring failures. For more effective repair of failures in JCP with heavy truck traffic, an innovative FDR technique with two layers of steel reinforcements and tie/dowel bars to adjacent JCPs was developed. The weak and poor base/subgrade layers were completely removed and replaced with concrete and steel reinforcements. Both longitudinal and transverse repair joints were designed considering the compatibility of concrete volume changes between the existing JCP slabs and repair slabs. Condition survey results indicated that the performance to date has been excellent with no visible distress under almost two years of the heavy truck traffic. For the repair of JCP sections with recurring failures, the implementation of the proposed technique with steel reinforcements and joint designs is expected to result in improved performance.

Study of the Temperature and Acoustic Emission Characteristics of the Concrete Hardening Process with Different Ways of Curing

Concrete is a basic building material. This article describes its properties. Microcracks result from volume changes in concrete. The intensity of temperature development and the way concrete is being cured have a significant influence on the emergence of microcracks. Indeed, the quantification of microcracks isn't simple. Using acoustic emissions it is possible to observe the evolution of scratches in hardening concrete - how many of them evolve and how the intensity of their emergence changes depending on different regimes of curing or different types of concrete (different cement batches, various additives and admixtures, etc.).

Effect of Curing on Roughness Development of Concrete Pavements

This paper deals with the results of a study on the effect of curing on as-constructed smoothness and subsequent roughness development of portland cement concrete pavements (PCCP) in Kansas. Ten test sections on five newly built PCCP projects on I-70 and I-135 were selected. At each site, one section was cured with a double application of curing compound as opposed to the single application currently specified. A section of equal length with single application was designated as the control section. Some sections were instrumented with thermocouples to collect temperature data at the bottom of the PCCP slab during construction. Large temperature gradients between the top and the bottom of the PCCP slab were observed during concrete placement. Double curing compound application tends to decrease this temperature gradient. Periodic longitudinal profile data was collected with a South Dakota-type profiler on the wheel paths of both driving and passing lanes on each section. From these profile data international roughness index (IRI) statistics were computed for each test section. Analysis of variance was performed to compare mean IRI values with respect to the curing compound application rate. It was found that the single curing compound results in lower as-constructed IRI values, but double application reduces roughness development in the long run, possibly due to lower differential autogenous volume change of concrete.

Variation of Crack Width over Time in Continuously Reinforced Concrete Pavement

The primary objective of this paper is to present the findings of field studies that investigated variations in crack widths over time in three continuously reinforced concrete pavement projects in Texas. Also presented are crack width variations through the slab depth. Vibrating wire gauges were installed at three slab depths—top, middle, and bottom—during concrete placement. Transverse cracks were induced at the locations of the gauges, and concrete strains were measured. The ages of the projects varied from 11 months to 2 years, 10 months. Significant variations existed in crack widths along the slab depth. Crack widths were largest at the top and smallest at the bottom. In the test sections of this study, crack widths at the middepth were about three-quarters of those at the top. Crack widths at the top and middepth were a direct function of temperature variations in the concrete at those depths. However, there was a poor correlation between concrete temperatures and crack widths at the bottom. There was clear evidence that moisture variations in concrete have substantial effects on concrete volume changes and crack widths. An immediate decrease in crack widths was observed after rains. Crack widths decreased over time within the time frame of this study. This finding is not consistent with the current theory on crack width variations over time, and further study is currently under way at the University of Texas at Austin to identify the causes. The findings will be reported as they become available.

Autogenous volume change of concrete at very early age

The autogenous volume change of concrete is defined as the external volume reduction caused by cement reactions. This type of volume reduction is often suspected to be the main cause of cracking in high performance concrete at early ages. However, the mechanisms of volume change and cracking are not well understood. The aims of this article are to make a theoretical analysis of the phenomenon, to quantify the most important parameters involved in the process, and to discuss the cases for which this type of shrinkage can cause cracking.

DEFORMATION AND DETERIORATION OF CONCRETE AT LOW TEMPERATURES

Under low temperature, some concrete structures suffer serious deterioration. This may be due to the ice formation in concrete micropores, which causes microcracking and induces volume changes of concrete. Based on this observation, we investigated deterioration of concrete subjected to cyclic cooling and heating of various temperature ranges. The two major findings are: (1) residual strain of concrete is in good correlation to its relative dynamic modulus of elasticity and (2) there are well-defined temperature ranges which determine the progress of deterioration. Qualitative and quantitative analyses will be made on these observations.

Applications of Orthotropic Decks in Bridge Rehabilitation

A bridge deck, subject to direct loading by heavy truck wheels and exposed to weather effects, is the most severely stressed structural element of a bridge. The static and dynamic effects of the moving wheel loads and the high ratio of live to dead load cause a wide range of alternating stresses in the deck. Repeated millions of times during the deck life, these stresses precipitate material fatigue. The decks are designed for standard loads stipulated in the AASHTO specifications. However, the actual wheel and axle loads are frequently much heavier and may cause severe overstress. Another significant contribution to flexural deck stresses is due to differential deflections of the supporting stringers, which is not addressed in the current design specifications for concrete decks. Exposure of the deck to wide temperature variations, moisture and freeze-thaw cycles further decreases the deck strength by causing concrete volume changes and cracking. However, the most important cause of deck deterioration is the action of deicing salts that penetrate concrete and corrode reinforcing steel. High pressures exerted by the rust cause further cracking, spalling and delamination of concrete, opening the way to more salt penetration and thus accelerating the irreversible process of concrete deck failure.

An experimental study of early thermal cracking in reinforced concrete

Synopsis Restrained volume changes in concrete can cause cracking before normal service loads are applied, since all concrete members undergo an early thermal cycle due to the heat of hydration. This mechanism of early thermal cracking is reviewed and an experimental laboratory investigation is described which tested the validity of the current proposals in BS 5337 for some different types, arrangements and amounts of reinforcement. Of the types of reinforcement investigated, the fabric was found, as expected, to give the best crack width control. It was confirmed that, provided a minimum ratio of reinforcement is present in reinforced concrete, thermal crack widths are a function of reinforcement ratio, reinforcement diameter, strength of concrete and bond strength between reinforcement and concrete.

1029 乾燥、湿潤にともなうコンクリートの内部湿度分布ならびに変形に関する研究 (第2報)

1029 乾燥、湿潤にともなうコンクリートの内部湿度分布ならびに変形に関する研究 (第2報)