scholarly journals Effects of Cyclic Freeze–Thaw on the Steel Bar Reinforced New-To-Old Concrete Interface

Molecules ◽  
2020 ◽  
Vol 25 (5) ◽  
pp. 1251
Author(s):  
Tao Luo ◽  
Chi Zhang ◽  
Xiangtian Xu ◽  
Yanjun Shen ◽  
Hailiang Jia ◽  
...  
Keyword(s):  
Compressive Strength ◽  
Shear Strength ◽  
Concrete Structures ◽  
Freezing Temperature ◽  
Frost Damage ◽  
Freezing And Thawing ◽  
Shear Properties ◽  
Freeze Thaw ◽  
Steel Bar ◽  
Concrete Interface

Frost damage of concrete has significant effects on the safety and durability of concrete structures in cold regions, and the concrete structures after repair and reinforcement are still threatened by cyclic freezing and thawing. In this study, the new-to-old concrete interface was reinforced by steel bar. The shear strength of the new-to-old concrete interface was tested after the new-to-old combination was subjected to cyclic freeze–thaw. The effects of the diameter of the steel bar, the compressive strength of new concrete, the number of freeze–thaw cycles and the freezing temperatures on the shear properties of new-to-old concrete interface were studied. The results showed that, in a certain range, the shear strength of the interface was proportional to the diameter of the steel bar and the strength of the new concrete. Meanwhile, the shear strength of the reinforced interface decreased with the decreasing of the freezing temperature and the increasing of the number of freeze–thaw cycles.

scholarly journals Experimental Study on Mechanical Properties and Pore Structure Deterioration of Concrete under Freeze–Thaw Cycles

Materials ◽  
2021 ◽  
Vol 14 (21) ◽  
pp. 6568
Author(s):  
Kai Zhang ◽  
Jing Zhou ◽  
Zhigang Yin
Keyword(s):  
Mechanical Properties ◽  
Compressive Strength ◽  
Pore Structure ◽  
Design Theory ◽  
Damage Model ◽  
Concrete Structures ◽  
Frost Damage ◽  
Dynamic Increase Factor ◽  
Freeze Thaw ◽  
Dynamic Compressive Strength

Understanding the evolution of mechanical properties and microscopic pore structure of concrete after freeze–thaw cycles is essential to assess the durability and safety of concrete structures. In this work, the degradation law of mechanical properties and damage characteristic of micro-structure of concrete with two water-cement ratios (w/c = 0.45 and 0.55) is investigated under the condition of freezing–thawing cycles. The influence of loading strain rate on dynamic compressive strength is studied. The microscopic pore structure after frost damage is measured by low-field nuclear magnetic resonance (LF-NMR) technique. Then, a damage model based on the porosity variation is established to quantitatively describe the degradation law of macroscopic mechanical properties. The test results show that the relative dynamic modulus of elasticity (RDME), dynamic compressive strength, flexural strength, and splitting tensile strength of concrete decrease with the increase of freeze–thaw cycles. Empirical relations of concrete dynamic increase factor (DIF) under the action of freeze–thaw cycles are proposed. Moreover, the experimental results of NMR indicate that the porosity as well as the proportion of meso-pores and macro-pores of concrete gradually increased with the increasing of freeze–thaw cycles. The research results can provide reference and experimental support for the anti-frost design theory and durability life prediction of hydraulic concrete structures in cold regions.

scholarly journals Degradation of Mechanical Behavior of Sandstone under Freeze-Thaw Conditions with Different Low Temperatures

2021 ◽  
Vol 11 (22) ◽  
pp. 10653
Author(s):  
Jingwei Gao ◽  
Chao Xu ◽  
Yan Xi ◽  
Lifeng Fan
Keyword(s):  
Compressive Strength ◽  
Elastic Modulus ◽  
Mechanical Behavior ◽  
Energy Absorption ◽  
Uniaxial Compressive Strength ◽  
Dynamic Strength ◽  
Freezing Temperature ◽  
P Wave ◽  
Freeze Thaw ◽  
P Wave Velocity

This study investigated the effects of freezing temperature under freeze-thaw cycling conditions on the mechanical behavior of sandstone. First, the sandstone specimens were subjected to 10-time freeze-thaw cycling treatments at different freezing temperatures (−20, −40, −50, and −60 °C). Subsequently, a series of density, ultrasonic wave, and static and dynamic mechanical behavior tests were carried out. Finally, the effects of freezing temperature on the density, P-wave velocity, stress–strain curves, static and dynamic uniaxial compressive strength, static elastic modulus, and dynamic energy absorption of sandstone were discussed. The results show that the density slightly decreases as temperature decreases, approximately by 1.0% at −60 °C compared with that at 20 °C. The P-wave velocity, static and dynamic uniaxial compressive strength, static elastic modulus, and dynamic energy absorption obviously decrease. As freezing temperature decreases from 20 to −60 °C, the static uniaxial compressive strength, static elastic modulus, dynamic strength, and dynamic energy absorption of sandstone decrease by 16.8%, 21.2%, 30.8%, and 30.7%, respectively. The dynamic mechanical behavior is more sensitive to the freezing temperature during freeze-thawing cycling compared with the static mechanical behavior. In addition, a higher strain rate can induce a higher dynamic strength and energy absorption.

THE EFFECTS OF SLOPE POSITION AND CROPPING SEQUENCE ON SOIL PHYSICAL PROPERTIES IN PRINCE EDWARD ISLAND

1988 ◽  
Vol 68 (4) ◽  
pp. 763-774 ◽  
Author(s):  
LINNELL M. EDWARDS
Keyword(s):  
Shear Strength ◽  
Hydraulic Conductivity ◽  
Prince Edward Island ◽  
Soil Depth ◽  
Aggregate Stability ◽  
Penetration Resistance ◽  
Slope Position ◽  
Bottom Slope ◽  
Freezing And Thawing ◽  
Freeze Thaw

Soil physical characteristics were examined at depth intervals of 0–15 and 15–30 cm over three slope positions (top-, mid-, and bottom-slope) for three cropping sequences (hay-barley, cereals-barley, and potato-barley). Hydraulic conductivity was a significant (P ≤ 0.05) 40–50% greater at top-slope than mid- or bottom-slope, and aggregate stability percentage was a significant 6–7% greater at bottom-slope than mid- or top-slope when the soil aggregates were pretreated by freezing and thawing (freeze/thaw). Under the potato-barley sequence shear strength, penetration resistance and bulk density were significantly greater than any other sequence by up to 29, 21 and 15%, respectively; while hydraulic conductivity and maximum penetration depth were, respectively, up to 65 and 28% lower than any other sequences. Under hay-barley, hydraulic conductivity and aggregate stability (freeze/thaw) were, respectively, up to a significant 82 and 10% greater than any other sequence. There was, therefore, significantly more compaction under potato-barley and more soil physical enhancement under hay-barley than other respective sequences. Disease severity was up to 55% greater at bottom-slope than at mid-slope or top-slope for Birka barley, which also showed a significant linear decrease (r2 = 0.89) in yield with increasing shear strength. Yield of Perth barley showed a significant linear increase with increasing soil depth (r2 = 0.92) and clay-silt content (r2 = 0.78). Key words: Aggregate stability (freeze/thaw), crop rotation, penetration resistance, shear strength, barley, potatoes, hay

scholarly journals Recycling of a Concrete Pavement after over 80 Years in Service

Materials ◽  
2020 ◽  
Vol 13 (10) ◽  
pp. 2262 ◽  
Author(s):  
Tomasz Rudnicki ◽  
Robert Jurczak
Keyword(s):  
Compressive Strength ◽  
Fatigue Testing ◽  
Heavy Traffic ◽  
Concrete Pavement ◽  
Petrographic Analysis ◽  
Concrete Aggregate ◽  
Freezing And Thawing ◽  
Traffic Loading ◽  
Freeze Thaw ◽  
Renewal Project

This article presents the results of fatigue testing and assessment of the mechanical and physical properties of the concrete pavement of the A6 motorway, which was put in service in 1938. After 82 years of operation under heavy traffic loading conditions, the pavement was fully recycled by crushing of the existing concrete and reuse of the reclaimed material in the new courses of pavement placed as part of the motorway renewal project. The main objective of this research was to determine the properties of the tested concrete, including compressive strength, water absorption and freeze-thaw resistance after 150 cycles of alternate freezing and thawing. The resistance of the concrete to the action of de-icing products was also checked. The article also presents the results of petrographic analysis of the aggregates. Additionally, concrete sampled from the pavement was evaluated for freeze-thaw resistance in relation to the determined porosity characteristics. The tested concrete, which was subjected to over 80 years of traffic loading on the A6 motorway, was found to meet the highest requirements as currently applied for the extra heavy-duty pavements. With a compressive strength value in excess of 50 MPa, the tested concrete can be rated at least CC40, according to EN 13877-2:2013-08. The samples were found to satisfy the freeze-thaw resistance requirements of an F150 rating. The air void analysis showed that the analyzed concrete contained 1.6% of micropores, i.e., air voids smaller than 300 μm (A300). The spacing factor, in turn, was below 0.200 mm (L = 0.185 mm). The example of the A6 motorway renewal project served to demonstrate that reclaimed concrete aggregate, obtained by crushing the entire pavement, can be used for production of the new pavement courses.

scholarly journals Physical and Mechanical Characteristics of Shallow Expansive Soil due to Freeze-Thaw Effect with Water Supplement

2021 ◽  
Vol 2021 ◽  
pp. 1-11
Author(s):  
Yanlong Li ◽  
Zili Wang ◽  
Yang Luo
Keyword(s):  
Shear Strength ◽  
Water Content ◽  
Expansive Soil ◽  
Freezing Temperature ◽  
Strength Reduction ◽  
Dry Density ◽  
Direct Shear ◽  
Soil Columns ◽  
Freeze Thaw ◽  
Shear Strength Reduction

Shear strength of shallow expansive soil varies along with the depth under the freeze-thaw effect. This work investigates shear strength characteristics of shallow expansive soil by simulating the actual freeze boundary conditions of seasonal frozen areas with water supplement. An integrated approach incorporating the freeze-thaw test and direct shear test was adopted. Firstly, unidirectional freezing tests for expansive soil columns under three different freezing temperature gradients were carried out. Secondly, direct shear tests under low vertical stress were performed on the standard samples, which were prepared by using cutting rings cut the thawed expansive soil columns into nine segments along with the depth. Temperature, water content, and dry density at different depths were also investigated after the freeze-thaw process. The test results showed that, after the freeze-thaw process, the shear strength of expansive soil columns showed significant differences along with the depth and highly correlated with water content, specifically the higher water content and the lower shear strength. The minimum shear strength in the expansive soil columns occurred at the soil layer below the frozen and unfrozen zones interface. The expansive soil column’s shear strength changed most under the moderate freezing temperature gradient corresponding to the most considerable shear strength reduction. Moreover, the significant decrease in cohesion was the main reason for the shear strength reduction of expansive soil after the freeze-thaw process. These results indicate significant depth variability in shear strength of expansive soil under the freeze-thaw effect.

Experimental Research on the Characteristics of Soil Strength Freeze-Thaw Weakening in Songhua River Songpu Bank

2014 ◽  
Vol 501-504 ◽  
pp. 403-409
Author(s):  
Xue Han ◽  
Zi Long Zhao ◽  
Zi Rui Gao
Keyword(s):  
Shear Strength ◽  
Internal Friction ◽  
Friction Angle ◽  
Soil Strength ◽  
Internal Friction Angle ◽  
Physical Parameters ◽  
Freezing And Thawing ◽  
Songhua River ◽  
Freeze Thaw ◽  
Soil Shear Strength

In order to study characteristics of soil strength freeze-thaw weakening in the Songhua River Songpu bank，basic physical parameters tests and triaxial compression tests were performed on that paragraph bank .The results showed that: after thawing the sample cohesion will drop substantially, the internal friction angle will increase greatly and soil shear strength will increase significantly; the cohesion of sample after repeated freezing and thawing will significantly decline，internal friction angle of soil will greatly increase，the soil shear strength will increase after the first freezing and thawing，with the increase in the number of freeze-thaw cycles, the soil shear strength will significantly decline. The results can provide Songhua slope stability analysis with a scientific basis.

Analysis of Freeze-Thaw Damage of Lightweight Aggregate Concrete

2009 ◽  
Vol 417-418 ◽  
pp. 829-832
Author(s):  
Ji Ze Mao ◽  
Koichi Ayuta ◽  
Hui Qi ◽  
Zong Min Liu
Keyword(s):  
Water Content ◽  
Coarse Aggregate ◽  
Lightweight Aggregate ◽  
Frost Damage ◽  
Lightweight Aggregate Concrete ◽  
Freezing And Thawing ◽  
Aggregate Concrete ◽  
Freeze Thaw ◽  
Expansion Pressure ◽  
Micro Cracks

Since lightweight aggregate usually accounts for a higher percentage of the concrete by volume, the properties of lightweight aggregate can significantly influence the properties of the resulting concrete. In this study, we investigated the effects of the water content of lightweight coarse aggregate (LCA) on freeze-thaw resistance of lightweight aggregate concrete (LC) and analyzed how to control the fatal frost damage - cracks in LC. The results showed that the freeze-thaw resistance of LC was determined by the water content of LCA. It is clear that lowering the water content of LCA below 17% is the key method to secure the freeze-thaw resistance of LC. The study showed that the higher the water content of LCA, the higher the weight loss and the larger pore volume of LCA, the bigger the length expansion and the lower the durability factors of LC after freezing and thawing. Internal cracks occurred only in the concrete specimens that contained LCAs with higher water content when subjected to freezing and thawing. Expansion pressure occurred easily in the higher water content LCAs and micro-cracks formed initially in the weak grains. Then micro-cracks enlarged and spread to the mortar as the number of freeze-thaw cycles increased. This process eventually caused LC expansion and damage.

scholarly journals Effect of Fibers on the Bond Behavior of Deformed Steel Bar Embedded in Recycled Aggregate Concrete

2020 ◽  
Vol 39 (4) ◽  
pp. 846-858
Author(s):  
Rashid Hameed ◽  
Usman Akmal ◽  
Qasim S. Khan ◽  
Muhammad Ahsan Cheema ◽  
Muhammad Rizwan Riaz
Keyword(s):  
Compressive Strength ◽  
Concrete Structures ◽  
Steel Fibers ◽  
Recycled Aggregates ◽  
Polypropylene Fibers ◽  
Reinforcing Bars ◽  
Bond Behavior ◽  
Pull Out ◽  
Steel Bar ◽  
Natural Aggregates

A large volume of concrete debris is being produced in many countries on the globe due to the demolition of old concrete structures and testing of concrete specimens in laboratories. One of the ways to reuse concrete debris is to produce Recycled Aggregates (RA) and use them in new concrete. In recent years, Recycled Aggregates Concrete (RAC) has experienced increasing demand in various non-structural and structural applications. In reinforced concrete structures, one of the sources of brittle failure is sudden loss of bond between reinforcing bars and concrete in anchorage zones. Therefore, for the structural application of any new kind of concrete such as fiber reinforced RAC, knowledge of bond characteristics of reinforcing bars embedded in concrete becomes essential for determining the overall structural response under different modes of loading. In this regard, this study experimentally investigated the effect of fibers on the bond stress-slip behavior of deformed steel re-bar embedded in RAC. Concrete mixes having 0, 50 and 100% RAs were prepared with and without the addition of fibers. Two types of fibers were investigated in mono form: hooked-ends steel and polypropylene fibers. The dosage of steel and polypropylene fibers was kept 40 and 4.4 kg/m3, respectively. Axial compression and standard pull-out tests were performed. Test specimens for pull-out test were prepared using deformed steel re-bars of 19mm (#6) diameter. The results of strength tests confirmed that the compressive strength of concrete is decreased by replacing Natural Aggregates (NA) with RAs. For bond behavior of steel re-bar, the results of this study showed that replacement of 50% NA with RAs did not affect the bond response of steel bar, however, 100% replacement of NA with RAs showed detrimental effect on bond stress slip behavior. The results further showed that the addition of both types of fibers made it possible to recover the loss in compressive strength, bond strengths and bond toughness occurred because of replacing NA with RAs. In case of RA concrete mixes containing hooked-ends steel fibers, strength values were found even greater than the strength values of Natural Aggregates Concrete (NAC). From the results of this study, it was found that it is possible to design a structural concrete mix using 100% RAs and steel fibers at relatively low dosage of 40kg/m3.

Impact Resistant Behavior of RC Beam Damaged by Freeze-Thaw Action

2016 ◽  
Vol 711 ◽  
pp. 745-750
Author(s):  
Yusuke Kurihashi ◽  
Maki Mizuta ◽  
Akinori Shimata ◽  
Norimitsu Kishi
Keyword(s):  
Compressive Strength ◽  
Elastic Modulus ◽  
Frost Damage ◽  
Rc Beam ◽  
Input Energy ◽  
Rc Beams ◽  
Freeze Thaw ◽  
Weight Impact ◽  
Falling Weight ◽  
The Impact

In this study, in order to investigate the impact resistant behavior of RC beams damaged by freeze-thaw action, falling-weight impact tests for RC beams were conducted taking with/without frost damage as variable. The RC beam used in this study has been damaged by accelerated freeze-thaw cycling. From this experiment, following results were obtained: 1) Elastic modulus and compressive strength of the concrete were decreased due to freeze-thaw action; 2) In the case of damaged beam, many fine cracks were occurred in small input energy; and 3) Deflections of damaged beam was larger than that of non-damaged beam at the same weight-falling height.

scholarly journals Interface Shear Strength at Various Joint Types in High-Strength Precast Concrete Structures

Materials ◽  
2020 ◽  
Vol 13 (19) ◽  
pp. 4364
Author(s):  
Young-Jin Kim ◽  
Won-Jong Chin ◽  
Se-Jin Jeon
Keyword(s):  
Compressive Strength ◽  
Shear Strength ◽  
Compressive Stress ◽  
Precast Concrete ◽  
Concrete Structures ◽  
High Strength ◽  
Curing Temperature ◽  
Interface Shear Strength ◽  
Interface Shear ◽  
Failure Loads

More precast concrete structures have recently been constructed due to their many advantages when compared to conventional cast-in-place construction. Structural behavior at the joints between the precast segments can significantly affect the overall integrity, safety, and serviceability of the structure. In this study, therefore, the interface shear strength of high-strength precast members was investigated by performing push-off tests with the following variables: compressive strength of precast members, dry or wet joint, number and height of shear keys, joint width, filler type, curing temperature, and lateral compressive stress. The test results were analyzed to reveal the effect of each test variable on the joint shear strengths of the specimens. For instance, the failure loads were increased by 14–140%, depending on the lateral compressive stress, as the specified compressive strength of the precast members was increased from 80 to 150 MPa in the dry joints. The failure loads of the wet joints strongly depended on the strength of the filler rather than on that of the precast members and, as a result, the specimen with ultra-high-strength concrete filler was 46–48% stronger than those with high-strength mortar filler. The shear strengths of various joint types obtained from the test were further analyzed in comparison with the predictive equations of Japan Society of Civil Engineers (JSCE) and American Association of State Highway and Transportation Officials (AASHTO) with the aim of validating the appropriateness of these design provisions. In particular, an improved value of a coefficient in the JSCE equation is proposed to cover a range of compressive strengths in various precast members and filling materials.

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