Simultaneous effects of salted water and water flow on asphalt concrete pavement deterioration under freeze–thaw cycles

The presence of water flow on road surfaces may lead to early deterioration of bituminous pavements. The adverse impacts of various anti-freezing materials on road surface performance have drawn the attention of many researchers. However, the simultaneous effects of salted water and water flow on the deterioration of road surfaces, particularly under freeze–thaw conditions, have not been adequately addressed. This research aims to study the combined effects of water flow and anti-freezing materials, which are usually present in the vicinity of asphaltic pavements during freeze–thaw cycles, on asphalt concrete deterioration. Two sets of asphalt concrete samples were prepared and subjected to six exposure states. The samples were also tested in an abrasion test apparatus and subjected to normal and frictional forces. Marshall strength loss and weight loss of the samples were measured and the results were analysed. The results indicated that the combined effects of water flow and de-icers under freeze–thaw conditions intensified the deterioration of asphalt concrete.     

Progress report 1992–1996

The effects of variation of cooling rate and time at minimum temperature on frost deterioration of concrete have been investigated on three non-air-entrained concrete and one air-entrained concrete. It was found that at an equal number of freeze/thaw cycles, the frost/salt scaling increased when reducing the rate of cooling for the non-air-entrained concretes. A slow cooling rate produced more scaling at comparable periods in the frozen condition, compared to a rapid cooling rate and variable time at minimum temperature. Air-entrained concrete with very good frost/salt durability showed no clear effect of freeze/thaw cycle variations. Measurements of resonance frequency at prolonged cycling for two of the concretes (same binder, with/without air) showed that for the airentrained concrete, the internal cracking was increased by increasing the rate of cooling. For the non-air-entrained concretes, the internal cracking was severe for all types of cycles. Measurements of absorption during the tests revealed increased absorption with increased damage and a strong correlation between absorption and internal cracking. The scaling was found to accelerate when internal cracking increased. The two types of deterioration (scaling and cracking) therefore appear to be connected in tests where both cracking and scaling occur. The results of this investigation illustrate an important difference between frost/salt scaling and internal cracking: scaling increased with a reduced rate of cooling, whereas internal cracking increased with an increased rate of cooling.     

Effect of the curing conditions of concrete on the behaviour under freeze–thaw cycles*

The aim of this work is to relate the curing conditions of concrete and the addition of an air‐entraining admixture with the damage caused by freeze–thaw cycles. In countries with a continental climate, the curing of concrete in summer is performed under climatic conditions of high temperature and low humidity, and during the winter the concrete suffers conditions of freeze–thaw, often accompanied by the use of de‐icing salts. This paper shows the experimental results of the behaviour of concrete specimens cured under climatic summer conditions (high temperature and low humidity) and then subjected to freeze–thaw cycles. Curing of the specimens includes conditions of good and bad practice in relation to wetting and protection of the concrete. It also examines the effectiveness of using an air‐entraining admixture in both cases. The experimental programme includes an evaluation of the mechanical properties of the concrete, the study of the cement hydration and the measurement of the volume and pore sizes of the concrete. These tests were performed before and after the application of the freeze–thaw cycles. The results obtained showed that the specimens without air‐entraining admixture show a deterioration of mechanical properties after the freeze–thaw test. However, the inclusion of air bubbles benefits the behaviour of concrete against freeze–thaw cycles so even better mechanical properties after the test were observed. This anomalous behaviour is because the cement hydration process continues over the freeze–thaw tests, closing the pore structure. This aspect has been confirmed with the DTA and TG tests performed.     

Evaluation of the combined deterioration by freeze–thaw and carbonation of mortar incorporating BFS,limestone powder and calcium sulfate

The durability performance of cementitious material is traditionally based on assessing the effect of a single degradation process. However, this study investigates the coupled deterioration properties of mortar incorporating industrial solid waste—ground granulated blast furnace slag (BFS) and different mineral admixtures, such as calcium sulfate (CS) and limestone powder (LSP). The combined deterioration properties caused by carbonation and frost damage in the mortar sample were experimentally investigated with respect to accelerated carbonation and freeze–thaw tests. Different degrees of deterioration, i.e. after subjected to 12, 30 and 60 freeze–thaw cycles, were induced in the freeze–thaw tests. The experimental investigation of single degradation revealed that the compressive strength, frost resistance and carbonation resistance decrease as the BFS replacement ratio increases by weight from 0 to 45%. The less amount of CH in the BFS cement leads to the carbonation progress more easily. Moreover, to achieve the same strength as ordinary Portland cement, 2 wt% CS and 4 wt% LSP in the BFS mortar are required. However, the data shows that incorporating LSP into the BFS mortar produces a lower frost resistance. The combined damage tests revealed that different deterioration degrees resulting from 12, 30 and 60 freeze–thaw cycles slightly decreased the carbonation resistance, which is related to the decrease in the inkbottle pore volume due to its water retention characteristics. Simultaneously, the pre-carbonation deterioration could effectively decrease the surface mass scaling of the freeze–thaw and the pore structure undergoes densification due to pre-carbonation.     

A preliminary study of RPC for repair and retrofitting materials

Abstract

This study aims to assess the performances of reactive powder concrete, RPC, as a new repair and retrofitting material and evaluate its durability in concrete members. One accelerated aging environment, namely a freeze‐thaw cycle acceleration deterioration test, was selected for the durability study of the repair materials. Before and after aging, the samples were evaluated by the bond strength (slant shear test), rebar pull out strength, and relative dynamic modulus NDT tests.

The test results show that the RPC displayed excellent repair and retrofit potentials, as it possessed high strengthening effect, bond strength, dynamic modulus and durability, as compared with other concretes. Using RPC or CFRP (carbon fiber reinforced plates) for strengthening concrete members one can obtain specific retrofit effects, but the costs are extremely different for these two materials.     

Engineering performance of a new siloxane-based corrosion inhibitor

This paper presents an evaluation of a new non-toxic corrosion inhibitor on selected engineering properties of concrete mixes with different cementitious materials following a corrosion and durability study on concrete samples. Corrosion inhibitors consist of powders or solutions which are added to concrete when mixed to prevent or delay corrosion of steel by their reaction with ferrous ions to form a stable and passive ferric oxide film on the steel surface. The new inhibitor functions slightly differently and its corrosion inhibition effect is due to the formation of a siloxane coating on the steel surface. Therefore, the performance of the new inhibitor in concrete mixes manufactured with CEM I, PFA and GGBS cements was compared against a well known and established corrosion inhibitor on the market, namely calcium nitrite in terms of their effect on workability (measured in terms of slump), compressive strength, freeze–thaw durability and macro-cell corrosion. The results from this experimental programme have demonstrated that the new inhibitor is effective in reducing or slowing down corrosion. In addition, it was found that CEM I concrete containing the new inhibitor was less penetrable to chlorides than that without. A similar set of results was obtained for the freeze–thaw resistance, but the compressive strength was found to decrease with the addition of the new inhibitor. In the case of concretes containing PFA and GGBS, the new inhibitor was found to be less effective. Further, long-term investigations are recommended to assess the effectiveness over time.     

A stochastic damage model for evaluating the internal deterioration of concrete due to freeze–thaw action

This paper presents a stochastic damage model for evaluating the internal deterioration of concrete due to freeze–thaw action, which involves great uncertainty and randomness. In this model, the structural element of concrete is discretized into infinite microelements, whose lifetimes are assumed to be independent random variables. Then expressions for the mean and variance of the damage of concrete are analytically derived. To calibrate the model parameters, a series of freeze–thaw tests in water on non-air-entrained concrete were conducted and back-calculation analyses were performed on the test results of dynamic modulus. The reliability of the proposed stochastic damage model is further validated through comparisons with the results of 80 other existing test specimens. The present model offers a theoretical basis for exploring the statistical aspect of concrete behavior during freeze–thaw.     

Investigation of freeze–thaw effects on mechanical properties of fiber reinforced cement mortars

Fibers are used for improving some properties of conventional concrete (which is a brittle material) such as tensile strength, abrasion resistance, absorption and crack control. This study investigates the usability of fibers against the harmful effects of freeze–thaw cycles on cement mortars. For this objective, five different types of fibers, i.e., Polypropylene (PP), Carbon (CF), Aramid (AR), Glass (GF) and Poly vinyl alcohol (PVA) in four different ratios (0.0%, 0.4%, 0.8% and 1.2%) were added to cement mortars along with an amount of air agent. These samples were then subjected to five different freeze–thaw cycles (0, 25, 50, 75 and 100). Thus, mechanical behaviors were investigated under freeze–thaw effects.The most important results of the study are summarized; the fibers increase flexural strength and deflection ability of the samples while decreasing compressive strength, dynamic modulus of elasticity and specific mass. The highest flexural strength was obtained with a 1.2% addition of CF fiber for the samples in normal conditions. The mechanical properties of the samples subjected to repetitive freeze–thaw cycles were also investigated; the best flexural strength was provided with 1.2% CF addition, while the highest dynamic modulus of elasticity was obtained with a 1.2% PP addition.     

Capillary suction model for characterizing salt scaling resistance of concrete containing GGBFS

This paper presents a rational method to characterize the freeze–thaw salt scaling performance of concrete based on capillary suction forces. The testing program included evaluating the concrete’s chemical chloride binding capacity, degree of hydration, total porosity, compressive strength, sorptivity and de-icer salt scaling resistance conducted at both, 28 days and 2 years. Mixtures consisted of paste and concrete containing 0–60% GGBFS as cement replacement, and a water-to-binder ratio of 0.31 or 0.38. The proposed capillary suction model was adapted to include the concrete’s chloride binding capacity, pore characteristics, and age. Results from the capillary suction model are found to correlate with experimentally measured ionic sorption coefficients. Results revealed that the capillary suction depth decreases with increasing percentages of GGBFS due to blocking of capillary pores as a result of the chemical interaction between the saline solution and the binder material. A freeze–thaw salt scaling resistance factor (F/T SSRF) is proposed which accounts for the concrete’s degree of hydration, sorptivity and tensile strength and is shown to correlate with the concrete’s cumulative mass loss tested in accordance with MTO LS-412. Accordingly, the salt scaling performance of concrete containing GGBFS is influenced by the combined effect of the concrete’s pore size distribution of the exposed surface, chloride binding capacity, degree of hydration, and tensile strength.     

Damaging effects of deicing chemicals on concrete materials

The damaging impact of various deicing chemicals and exposure conditions on concrete materials was investigated. Five deicing chemicals (sodium chloride, calcium chloride with and without a corrosion inhibitor, potassium acetate, and an agricultural product) were studied. Freezing–thawing (F–T) and wetting–drying (W–D) exposure conditions were considered. Mass loss, scaling, compressive strength, chemical penetration, and micro-structure of the paste and concrete subjected to these deicing chemicals and exposure conditions were evaluated. Results indicated that the various deicing chemicals penetrated at different rates into a given paste and concrete, resulting in different degrees of damage. Among the deicing chemicals tested, two calcium chloride solutions caused the most damage. Addition of a corrosion inhibitor into the calcium chloride solution delayed the onset of damage, but it did not reduce the ultimate damage. Chloride-related deicing chemicals often brought about leaching of calcium hydroxide, as well as chemical alterations in concrete. Potassium acetate caused minor scaling, associated with alkali carbonation of the surface layer of concrete. Although producing a considerable number of micro-pores on the surface of the samples, the agricultural deicing product resulted in the least chemical penetration and scaling damage of paste and concrete.     

Durability and water absorption properties of surface treated concretes

Durability of concrete can be improved by applying surface treatments. Pore-lining treatments prevent or delay the ingress of water-borne salts while allowing vapour transfer across the concrete surface. The most common pore-liners are silanes and siloxanes; both reported to give good results. One area of concern, however, is variability in effectiveness of the treatment. This variability may be due to inconsistent coverage or extreme drying conditions. With care these can be controlled but another source of variability which is difficult to control is the moisture profile within the concrete at the time of application of the treatment. This paper describes a test programme to assess the sensitivity of three different surface treatments to moisture gradient in the concrete at the time of application of treatment. The test programme included durability parameters such as chloride ingress, corrosion due to chloride ingress, freeze–thaw salt scaling resistance. Water absorption (sorptivity) of treated and untreated concretes was also measured with a non-distructive test technique called Autoclam with the aim of determining if the Autoclam sorptivity test can be used to assess the effectiveness of surface treatments. Using these results it is possible to avoid, or allow for, moisture conditions which would adversely affect the success of a pore-liner. However there are advantages in specifying an expected performance of the surface treatment rather than specifying the conditions in which it must be placed. By this method a treatment would have to achieve a specified value of sorptivity or a specified reduction in sorptivity. Failure to do so would be an objective basis on which to make a decision of whether or not to reject the treatment. The Autoclam is a device capable of measuring sorptivity values down to the range typical of surface treated concrete. The paper assesses if the device can be used to discriminate between acceptable treatment and unsatisfactory treatments.     

Microscopic analysis of paste and aggregate distresses in pervious concrete in a wet, hard freeze climate

In a recent survey, the durability and condition of 29 in service pervious concrete pavements built in a wet, hard freeze environment were assessed, and 33 core samples were collected. Following up on this survey, this paper identifies some of the common subsurface distresses observed in the core samples with optical microscopy instruments. In the distressed samples, cracks went through the aggregate, paste, and interfacial transition zone (ITZ). The cracks were similar to cracks in conventional concretes that formed due to known freeze/thaw damage. In addition to cracking patterns, it was discovered that none of the 33 pervious concrete samples contained the recommended quantity or spacing of entrained air bubbles. There was a lack of entrained air bubbles despite the addition of air-entraining admixtures to all of the pervious concrete mixtures. It is unknown if the lack of entrained air bubbles contributed to the cracks in the pervious concretes.     

Effect of freeze–thaw cycles on durability and strength of very soft clay soil stabilised with recycled Bassanite

This paper investigates the influence of freeze–thaw cycles on the unconfined compressive strength and durability of very soft clay soil stabilised with recycled Bassanite, which is produced from gypsum wastes. The results of this study show that an increase in the number of freeze–thaw cycles decreases the unconfined compressive strength and durability index. The presence and increase in the Bassanite content in the soil mixture has a significant effect on the improvement of strength, volume change and durability of samples subjected to freeze–thaw cycles. The role of Bassanite in increasing the soil strength and durability is more significant in the case of samples exposed to freeze–thaw cycles compared to those not exposed to freeze–thaw cycles. The dry unit weight increased, and moisture content decreased with the increase of Bassanite content in the soil mixture. The effect of freeze–thaw cycles on the dry unit weight and moisture content is insignificant compared to unexposed samples. The maximum volumetric changes occurred in the first freeze–thaw cycle, and afterward, the volume changes decreased with an increase in freeze–thaw cycles. The use of recycled Bassanite obtained from gypsum wastes as a stabiliser material for very soft clay soil achieves the acceptable durability and strength against the effects of freeze–thaw cycles.     

Durability studies on steelmaking slag concretes

Electric-arc furnace slag is proposed as a substitute for the conventional aggregate used in classical structural concrete. In the present research is studied the durability of these slag aggregate concretes and their resistance to both physical (freeze–thaw, high temperature and relative humidity) and chemical degradation (sulfate attack, alkali–aggregate reaction and marine environment), as well as their resistance to the corrosion of steel reinforcement bars (an assessment of the risks of corrosion) embedded in the concrete matrix. This approach requires laboratory studies. The main objective of this work focuses on evaluating the durability of slag concrete under the conditions specified in the Spanish structural concrete code. In general terms, the behavior of the concrete with slag aggregate was similar to or better than the reference concrete (natural aggregate), except in case of exposure to marine environments and seawater, which resulted in quicker chloride penetration. The study confirms the viability of producing steel-reinforced concrete with slag aggregate.     

Dimensional and ice content changes of hardened concrete at different freezing and thawing temperatures

Samples of concrete at different water-to-cement ratios and air contents subjected to freeze/thaw cycles with the lowest temperature at about ?80 °C are investigated. By adopting a novel technique, a scanning calorimeter is used to obtain data from which the ice contents at different freeze temperatures can be calculated. The length change caused by temperature and ice content changes during test is measured by a separate experiment using the same types of freeze–thaw cycles as in the calorimetric tests. In this way it was possible to compare the amount of formed ice at different temperatures and the corresponding measured length changes. The development of cracks in the material structure was indicated by an ultra-sonic technique by measuring on the samples before and after the freeze–thaw tests. Further the air void structure was investigated using a microscopic technique in which air ‘bubble’ size distributions and the so-called spacing factor, indicating the mean distance between air bubbles, were measured. By analyzing the experimental result, it is concluded that damages occur in the temperature range of about ?10 °C to ?55 °C, when the air content is lower than about 4% of the total volume. For a totally water-saturated concrete, damages always occur independently of the use of entrained air or low water-to-cement ratios. It is, further, concluded that the length changes of these samples correspond to the calculated ice contents at different temperatures in a linear fashion.     

Freezing and de-icing salt resistance of blast furnace slag concretes

This paper presents the results on investigations made into a concrete containing cement rich in granulated blast furnace slag (57%). Whereas slag cement concretes have proved successful in structures subjected to chemical attack, their use in structures subjected to freezing and de-icing salt attack is a problem of numerous investigations. The results concerning water/cement ratio and air content in concrete mixtures are presented in this paper. The effect of polypropylene microfibre addition to the concrete was also analysed. The research shows that air entraining the concrete mix up to the level of 5–6% guarantees obtaining high resistance to the action of de-icing agents, even at relatively high values of water/cement ratio. Apart the air content, the addition of microfibre to the concrete mixture was highly effective. For these samples scaling was the lowest. Phase composition investigations confirm that calcite and aragonite (as the carbonation products) were present on the surface of concrete.     

Evaluation of Portland limestone cements for use in concrete construction

The paper describes a study carried out to examine the performance of concrete produced using combinations of Portland cement (PC) and limestone (LS), covering compositions for Portland limestone cement (PLC) conforming to BS EN 197-1: 2000, and up to 45% LS. In particular, key engineering (mechanical) and durability properties of concrete were studied. The results indicate only minor differences in performance between PC and 15% PLC concretes of the same cement content and water/cement (w/c) ratio (cement = Portland cement + addition). However, there was an adverse effect with increasing LS content beyond 15% of the cement content for many properties. It is shown that for 35 N/mm² cube strength concrete the adjustment to w/c ratio to match the compressive strength of PC concrete was in the region of 0.08 for each 10% LS added (water curing at 20°C) above this level. Studies of permeation and concrete durability performance, including, initial surface absorption, carbonation resistance, chloride diffusion, freeze/thaw scaling and abrasion resistance, indicate that in general the test concretes followed single relationships with strength for most properties. Consideration is given to the practical implications of the main outcomes of the study.     

Freeze-thaw and deicing salt resistance of concrete testing by the CDF method CDF resistance limit and evaluation of precision

RILEM TC 117-FDC decided unanimously that the precision of any freeze-thaw and deicing test procedure must be assessed in accordance with ISO 5725. In addition, a resistance limit for concrete should be approved with respect to practical performance. In this article it is shown that these requirements are fulfilled by the CDF test (capillary suction of deicing chemicals and freeze-thaw test). To verify this, different compositions covering the design rules as defined by standards and given by long-term experience have been measured. The repeatability covering the scatter of the materials and the test procedures was calculated using a large data base of 400 tests. To determine the reproducibility, which includes repeatability and between laboratory scatter, 26 comparison tests between two universities, one internal and two European round robin tests were evaluated additionally. The mean scaling after 28 cycles (14 days) at 1500 g m^?2 proved to be a reliable CDF resistance limit. At this level a coefficient of variation for repeatability has been established at 11% and for reproducibility at 18%. An acceptance criterion may be proposed for further discussion at 1800 g m^?2 as the upper 5% fractile. This minimizes the risk for both customer and supplier.     

Freezing of air-entrained cement-based materials and specific actions of air-entraining agents

The freeze–thaw resistance of all cement-based materials is improved by incorporating a fine air bubble system in them. For acceptable life expectancy, incorporated air bubble volume should be about 25% of the cement paste. The specific surface of the air bubble system need to be above 25 mm²/mm³ and a spacing factor below about 0.16 mm. Powers explained these on the basis of his saturated flow hydraulic pressure mechanism. According to Powers’ mechanism, the chemical nature of the air-entraining agent has no part in this improvement in performance.Helmuth, one of the principal co-workers of Powers, has questioned a number of assumptions of Powers’ mechanism. Most importantly, Helmuth showed that ice penetrates concrete as dendritic crystals. Furthermore, a number of workers have shown that the chemical nature of the air-entraining agent affects the freeze–thaw resistance of cement-based materials. Some air-entraining agents do not improve the freeze–thaw resistance even though they entrain air of the required characteristics.In this paper, a modified and expanded version of Helmuth’s model of ice penetration in concrete is utilised to explain the action of air bubbles. All air bubbles contain a layer of water on their inner surfaces. Surface tension spreads out water in the air bubbles as annular layers. Air-entraining agents may form or precipitate hydrophobic layers on air bubble surfaces. When an ice dendrite reaches an air bubble, the annular water layer freezes to an annular layer of ice. The hydrophobic layer on the air bubble surface reduces the ice–paste bond. Under this circumstance, the ice layer within the air bubble grows. During this growth, water is withdrawn from the surrounding by suction. A water movement under suction does not produce any expansive pressure. Withdrawal of water to the air bubbles explains the beneficial action of air entrainment. The specific efficiency of air-entraining agents is explained by the different degree of hydrophobicity produced by air-entraining agents.     

Strength and durability performance of concrete axially loaded members confined with AFRP composite sheets

The performance of concrete columns externally wrapped with aramid fiber reinforced polymer composite sheets is presented in this paper. The confined and unconfined (control) specimens were loaded in uniaxial compression. Axial load and axial and hoop strains were measured in order to evaluate stress–strain behavior, ultimate strength, stiffness, and ductility of the wrapped specimens. Results show that external confinement of concrete by fiber reinforced polymer (FRP) composite sheets can significantly enhance strength, ductility and energy absorption capacity. An analytical model developed earlier by the author to predict the entire stress–strain response of concrete specimens wrapped with FRP composite sheets was applied. Comparison between the experimental and analytical results indicates that the model provides satisfactory predictions of the stress–strain response. The paper also presents the performance of the wrapped concrete specimens subjected to severe environmental conditions such as wet–dry and freeze–thaw cycles. The specimens were exposed to 300 cycles of wetting and drying using salt water. Results show that specimens wrapped with aramid fibers experienced no reduction in strength due to wet/dry exposure, but some reduction was observed due to freeze/thaw exposure.