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

2016 ◽  
Vol 691 ◽  
pp. 14-27
Author(s):  
Robert Sonnenschein ◽  
Juraj Bilčík ◽  
Katarína Gajdošová
Keyword(s):  
Drying Shrinkage ◽  
Peak Level ◽  
Parameter Analysis ◽  
Early Age ◽  
Reinforcing Bars ◽  
Volume Changes ◽  
Concrete Element ◽  
Thermal Movement ◽  
Cover Thickness ◽  
Crack Widths

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.

Influence of Early Age Volume Changes on Long-Term Concrete Shrinkage

1998 ◽  
Vol 1610 (1) ◽  
pp. 28-32 ◽  
Author(s):  
Erika E. Holt ◽  
Donald J. Janssen
Keyword(s):  
Concrete Slab ◽  
Drying Shrinkage ◽  
Early Age ◽  
Volume Changes ◽  
Test Procedures ◽  
Cracking Behavior ◽  
Concrete Shrinkage ◽  
Cracking Potential ◽  
Partially Restrained

Volume changes can occur in concrete during the first 24 hr and are generally missed in laboratory shrinkage evaluations. Unfortunately these early age volume changes are present in real pavements and structures and can contribute to the cracking behavior of the concrete at later ages. Early age volume changes can occur in two forms: drying shrinkage before the start of curing and autogenous volume changes. Although these early age volume changes are often dismissed as being insignificant, recent work in Europe has identified magnitudes for early age volume changes of some concretes that are equal to or greater than 28-day drying shrinkage measurements. Expansions have also been identified in some cases. The results of some investigations of volume changes in concrete during the first 24 hr under both drying and nondrying conditions are presented. An example of potential long-term cracking under partially restrained conditions (concrete slab-on-grade modeled by a concrete ring cast around a hollow steel ring) is used to illustrate the magnitude of influence of early age volume changes on concrete cracking. Both test procedures employ nonstandard methods to quantify the cracking potential of concrete.

scholarly journals Causes of Early-Age Thermal Cracking of Concrete Foundation Slabs and their Reinforcement to Control the Cracking

2017 ◽  
Vol 25 (3) ◽  
pp. 8-14 ◽  
Author(s):  
Juraj Bilčík ◽  
Róbert Sonnenschein ◽  
Natália Gažovičová
Keyword(s):  
Environmental Impact ◽  
Thermal Cracking ◽  
Effect Of Temperature ◽  
Early Age ◽  
Mass Concrete ◽  
Volume Changes ◽  
Interaction Models ◽  
Concrete Foundation ◽  
Temperature Loads ◽  
Crack Widths

Abstract This paper focuses on the causes and consequences of early-age cracking of mass concrete foundation slabs due to restrained volume changes. Considering the importance of water leaking through cracks in terms of the serviceability, durability and environmental impact of watertight concrete structures, emphasis is placed on the effect of temperature loads on foundation slabs. Foundation slabs are usually restrained to some degree externally or internally. To evaluate the effect of external restraints on foundation slabs, friction and interaction models are introduced. The reinforcement of concrete cannot prevent the initiation of cracking, but when cracking has occurred, it may act to reduce the spacing and width of cracks. According to EN 1992-1-1, results of calculating crack widths with local variations included in National Annexes (NAs) vary considerably. A comparison of the required reinforcement areas according to different NAs is presented.

scholarly journals Influence of compressive strength and maturity conditions on shrinkage of ordinary concrete

2021 ◽  
Vol 13 (6) ◽  
pp. 168781402110244
Author(s):  
Olga Szlachetka ◽  
Joanna Witkowska-Dobrev ◽  
Marek Dohojda ◽  
Anna Cała
Keyword(s):  
Compressive Strength ◽  
Portland Cement ◽  
Drying Shrinkage ◽  
Point Of View ◽  
Early Age ◽  
Volume Changes ◽  
Ordinary Concrete ◽  
Dry Conditions ◽  
Total Elimination

The paper presents results of investigations of compressive strength and shrinkage of concrete samples made on the basis of the Portland cement CEM I 32.5R, after 2, 7, 14, 28, 90, and 365 days of maturation in four different maturation conditions. It was shown that after 28 days the samples cured according to the standard in the cuvettes with water achieved the highest compressive strength, although the early-age compressive strengths after 7 and 14 days were lower than those for the samples cured in building film and in dry conditions. A determined correlation between the compressive strength and shrinkage of the concrete proves that wet curing also allows a total elimination of the shrinkage in the first 28 days. Along with the growth of the compressive strength, the drying shrinkage reduces. Obtained results confirmed that the best way of concrete curing, among the analyzed methods, from the point of view of both compressive strength and volume changes is the wet curing.

scholarly journals Autogenous and drying shrinkage of mortars based on Portland and calcium sulfoaluminate cements

2020 ◽  
Vol 53 (5) ◽  
Author(s):  
Davide Sirtoli ◽  
Mateusz Wyrzykowski ◽  
Paolo Riva ◽  
Pietro Lura
Keyword(s):  
Portland Cement ◽  
Water Demand ◽  
Ordinary Portland Cement ◽  
Rapid Evolution ◽  
Autogenous Shrinkage ◽  
Drying Shrinkage ◽  
High Water ◽  
Early Age ◽  
Volume Changes ◽  
Calcium Sulfoaluminate

Abstract Calcium sulfoaluminate (CSA) cement can be used as an alternative binder in concrete, partially or fully replacing ordinary Portland cement. While CSA cement considerably accelerates the mechanical properties development, the rapid evolution of the microstructure together with the high water demand cause rapid and large volume changes at early ages. As volume changes may lead to early-age cracking, measures to reduce them may be required In this paper, autogenous and drying shrinkage are studied in mortars prepared with Portland cement, CSA cement or a 50/50 blend as binder. Very fast self-desiccation and high autogenous shrinkage of the CSA-based mortar were observed compared to the mortar made with Portland cement. On the other hand, the early-age volume changes can be limited if a blend of the two cements is used. The blended system revealed a bi-modal trend in the evolution of self-desiccation and autogenous shrinkage, in which the initial fast self-desiccation and shrinkage enter the dormant phase after the first couple of days and again start after about 28 days.

scholarly journals Updating Carbon Storage Capacity of Spanish Cements

2018 ◽  
Vol 10 (12) ◽  
pp. 4806 ◽  
Author(s):  
Carmen Andrade ◽  
Miguel Sanjuán
Keyword(s):  
Carbon Storage ◽  
Storage Capacity ◽  
Concrete Cover ◽  
Raw Material ◽  
Cement Clinker ◽  
Reinforcing Bars ◽  
Concrete Element ◽  
Length Of Service ◽  
Carbonation Reaction ◽  
Carbon Dioxide Uptake

The fabrication of cement clinker releases CO2 due to the calcination of the limestone used as raw material, which contributes to the greenhouse effect. The industry is involved in a process of reducing this amount liberated to the atmosphere by mainly lowering the amount of clinker in the cements. The cement-based materials, such as concrete and mortars, combine part of this CO2 by a process called “carbonation”. Carbonation has been studied lately mainly due to the fact that it induces the corrosion of steel reinforcement when bringing the CO2 front to the surface of the reinforcing bars. Thus, the “rate of carbonation” of the concrete cover is characterized by and linked to the length of service life of concrete structures. The studies on how much CO2 is fixed by the hydrated phases are scarce and even less has been studied the influence of the type of cement. In present work, 15 cements were used to fabricate paste and concrete specimens withwater/cement (w/c) ratios of 0.6 and 0.45 which reproduce typical concretes for buildings and infrastructures. The amount of carbon dioxide uptake was measured through thermal gravimetry. The degree of carbonation, (DoC) is defined as the CO2 fixed with respect to the total theoretical maximum and the carbon storage capacity (CSC) as the carbonation uptake by a concrete element, a family or the whole inventory of a region or country. The results in the pastes where analyzed with respect to the uptake by concretes and indicated that: (a) the humidity of the pores is a critical parameter that favours the carbonation reaction as higher is the humidity (within the normal atmospheric values), (b) all types of cement uptake CO2 in function of the CaO of the clinker except the binders having slags, which can uptake additional CO2 giving aDoC near or above 100%. The CSC of Spain has been updated with respect to a previous publication resulting in proportions of 10.8–11.2% of the calcination emissions, through considering a ratio of “surface exposed/volume of the element” of 3 as an average of the whole Spanish asset of building and infrastructures.

scholarly journals Early-Age Properties of Concrete Based on Numerical Hydration Modelling: A Parametric Analysis

Materials ◽  
2020 ◽  
Vol 13 (9) ◽  
pp. 2112 ◽  
Author(s):  
Marco Pepe ◽  
Carmine Lima ◽  
Enzo Martinelli
Keyword(s):  
Parametric Analysis ◽  
Thermal Stresses ◽  
Cement Hydration ◽  
Concrete Strength ◽  
Numerical Procedure ◽  
Early Age ◽  
Concrete Element ◽  
Curing Conditions ◽  
Simplified Approach ◽  
Mechanical Performances

The early-age performances of cement-based mixtures are governed by cement hydration reactions. As a matter of fact, the heat generated during the setting and hardening phases due to the hydration processes increases the temperatures within the concrete elements while it starts developing its mechanical properties. These thermal stresses can cause the premature cracking of the cementitious matrix and undermine the long-term durability of the whole concrete element, especially in the case of massive structures where the dissipation of generated heat is more difficult. It is worth highlighting that the kinetics of cement hydration is mainly governed by the mixture composition; on the other hand, the heat generated during the setting and hardening is also influenced by the geometry of the element and/or its curing conditions. In this context, this study presents a numerical procedure intended to simulate the hydration reactions, and hence scrutinize the development of concrete properties at the early-age. Specifically, considering the variation of several factors, such as concrete strength class, element size and curing conditions, a comprehensive parametric analysis is presented herein, leading to the proposal of a simplified approach for both predicting the time evolution of the concrete mechanical performances at the early-age and mitigating the risk of premature cracking.

Influence of transverse crack width on reinforcement corrosion initiation and propagation in mortar beams

2008 ◽  
Vol 35 (3) ◽  
pp. 236-245 ◽  
Author(s):  
Mustafa Şahmaran ◽  
İ. Özgür Yaman
Keyword(s):  
Diffusion Coefficient ◽  
Effective Diffusion Coefficient ◽  
Crack Width ◽  
Effective Diffusion ◽  
Reinforcing Bars ◽  
Nacl Solution ◽  
Accelerated Corrosion ◽  
Corrosion Initiation ◽  
Initiation And Propagation ◽  
Crack Widths

This paper discusses the relationship between crack widths, chloride diffusivity, and corrosion rate of cracked mortar beams. Flexural loads are introduced to generate crack widths ranging from 29 to 390 µm. The specimens were subjected to accelerated corrosion by immersion in a 5% NaCl solution and a constant voltage of 12 V. In addition, salt ponding tests were conducted to determine the chloride ion transport properties. The results showed that as the crack width increased, the effective diffusion coefficient (corrosion initiation) and mass loss of steel reinforcing bars due to the accelerated corrosion (corrosion propagation) also increased. For crack widths less than about 135 µm, the effect of crack width on the effective diffusion coefficient and mass loss of steel reinforcing bars embedded in mortar specimens was found to be marginal when compared with the virgin specimens. Therefore, it was concluded that the effect of crack width on the corrosion initiation and propagation period was more pronounced when the crack width is greater than about 135 µm. Moreover, a significant amount of self-healing was observed for the cracks that have widths below 50 µm when subjected to the NaCl solution exposure.

The Early-Age Drying Shrinkage of Cement-Based Materials with the same Workability after Temperature Compensation

2013 ◽  
Vol 405-408 ◽  
pp. 2604-2609
Author(s):  
Li Feng Zhang ◽  
Jun Ying Lai ◽  
Xiao Qian Qian ◽  
Chong Shen
Keyword(s):  
Temperature Compensation ◽  
Setting Time ◽  
Drying Shrinkage ◽  
Concrete Specimen ◽  
Temperature Deformation ◽  
Control Group ◽  
Early Age ◽  
Peak Time ◽  
Initial Setting Time ◽  
Cement Based Materials

The early age drying shrinkage of cement-based materials with same the same workability staring from the initial setting time was studied. Superplasticizers (SP) were used to get the same workability. The drying shrinkage of paste was measured by clock gauge, and CABR-NES deformation instrument was used to measure the shrinkage of concrete. Temperature probes were buried into both paste and concrete specimen cores to measure the temperature curve, and temperature deformation was considered into the early shrinkage. Results show the addition of SP increases much more shrinkage than the control group, and polycarboxylate SP increases more shrinkage than naphthalene SP. The different temperature peak time of different mixtures show that the addition of SP changes the hydration process of cement, and the shrinkage of cement-based materials after temperature compensation is bigger than the measured value in the first 6 hours, but the gap is not big.

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