Combined salt and frost attack is a major durability problem in concrete highway pavements in the state of Michigan, USA, where road-salts are used extensively for ice melting purposes. Previous studies have shown that continuous measurement of length-change during a freeze-thaw cycle is an effective tool in indentifying frost mechanisms. In this study the focus was to evaluate the cryogenic suction effect on frost expansion. The net frost expansion (linear dilation) was determined by monitoring the change in length of air-entrained concrete specimens undergoing a freeze-thaw cycle between 20 °C and -20 °C. Two dilation processes were found during freezing, an initial dilation at the freezing point (independent of surface exposure liquid), and a subsequent dilation, which is only found when a salt solution is present on the surface. Specimen expansion continues during the entire freezing period, including a 3 hour ramp at constant temperature (-20 °C). This secondary dilation dominates when the surface is exposed to a deicer solution. At constant temperature below initial freezing point, cryogenic suction of surface liquid (i.e., 3% salt solution) was found to be a major factor in sub-zero liquid transport that causes frost expansion in concrete. During this process, air voids are being filled as well and air is being displaced. Some air near the surface can escape. This was observed at -20 °C where escaping air was trapped in the liquid surface layer.

This paper describes the findings of a recently completed investigation by the University of Michigan to identify the causes for premature, mid-slab cracking of joined plain concrete pavement (JPCP) in Michigan. The study found several factors are working interactively to induce slab cracking. The major factor is the support characteristics of the unbound open-graded aggregate base. Deflection testing showed a permanent loss of slab contact with the base (void) exists near the doweled joint. Time history analysis of the deflection data showed that the dowels are very likely loose. Loss of slab-base contact without pumping suggests that post-compaction under heavy vehicle loading or particle degradation is occurring. In addition, the study found that the load transfer efficiency (LTE) across joints has declined since construction. Finite element analysis (ABAQUS) was used to evaluate the extent and significance of these factors on tensile stress and fatigue cracking. Fatigue failure culminates from excessive tensile stress at mid-slab at the slab's topside outer edge. The slab stress predictions correlate well with the deflection-based fatigue model by Wu et al. (1993) suggesting that a threshold corner deflection criteria may be used to determine when loss of slab support is critical.

Internal stresses are present in Portland cement concrete pavement at early ages due to restrained curling and axial contraction. The risk of cracking in the pavement is largely associated with the temperature and tensile strength development of the concrete mixture as it cures. The temperature development is heavily influenced by heat released during cement hydration, the temperature of the concrete ingredients, and daily and seasonal fluctuations in ambient temperature. It has been observed that thermal stress development is most severe when the peak in the heat developed from hydration coincides with maximum daily ambient temperature. Thus, consideration should be given to placing concrete in the late afternoon or evening, especially during summer time placing conditions.

Hydrophobic impregnation is a well-known method to reduce water absorption and improve the corrosion resistance of reinforced concrete. However, its effectiveness in enhancing the freeze-thaw resistance of concrete remains unclear. This study aims to evaluate the impact of two hydrophobic impregnation methods, surface impregnation (SIP) and internal impregnation (IIP), on the long-term freeze-thaw (F-T) resistance of concrete. The results demonstrate that the IIP increased the air content of fly ash-based concrete by 20%-93% and reduced the compressive strength by 10%-15%. Both SIP and IIP are effective in resisting water penetration under isothermal conditions but ineffective in preventing pumping during F-T cycles and eventually lead to oversaturation and frost damage. The surface-impregnated concrete shows severe scaling in the long term, while the internally impregnated concrete is damaged both externally and internally soon after reaching critical saturation. The study demonstrates that hydrophobic impregnation does not benefit concrete with good F-T resistance, and maintaining a hydrophilic pore structure is crucial to ensure the free flow of water and the normal functioning of the air void system. The results also suggest that salt frost scaling shares a similar mechanism with regular F-T attacks, both of which depend on the pore structure and the quality of the air void system.

This study presents preliminary findings from an ongoing Federal Highway Administration project investigating the impact of increased Portland Cement Concrete (PCC) strength, among other properties, on the performance of PCC pavements. Traditionally, PCC pavement specifications have prioritized aggregate gradation, flexural strength, compressive strength, and air content as indicators of quality. However, this research suggests that other PCC properties could also serve as significant predictors of long-term pavement performance. Through a detailed literature review and preliminary analysis of the Long-Term Pavement Performance data, this paper aims to (1) identify high-strength PCC properties associated with superior pavement performance, particularly in terms of durability near joints and edges; (2) identify testing methods to quantify these properties; and (3) develop revised mix design procedures to produce pavements with these beneficial properties while still satisfying economic and construction requirements. The study observes general trends in PCC strength across different climates and explores their implications for pavement performance, including distress modes such as spalling, faulting, and overall roughness. Initial models for predicting these distresses are presented, highlighting the complex interplay between PCC properties, environmental conditions, and pavement performance. These findings aim to guide the development of more durable and predictable PCC pavements, with further research needed to validate the observed trends and refine predictive models. (Abstract generated by AI tool ChatGPT 4)

It is generally believed that slab warping uplift in Jointed Plain Concrete Pavements (JPCP) is caused by drying shrinkage moisture gradients that develop within the top region of a slab cross section. Field experience has shown that excessive moisture warping uplift of joints can develop if a slab on grade is exposed simultaneously to drying at the top and moisture at the bottom surface. The results from this study show that internal self-desiccation causes a uniform reduction in humidity within a cross section for a sealed curing condition. This renders the cross section prone to moisture warping if either the top or bottom surface is exposed to water. Thus, drying at the top and wetting at the bottom create a moisture gradient that causes increased moisture warping uplift. This was verified from beam uplift tests.

Frost resistance of concrete is highly related to air void system quality and moisture transport behavior in concrete, which are affected by multiple factors. In this study, different lightweight aggregate contents, water/binder ratios, and three types of supplementary cementitious materials were adopted to investigate the effects on frost resistance of concrete, along with mechanical properties, air void system, and transport properties. It was found that lightweight aggregate reduced compressive strength at an early age and increased air content and total moisture uptake due to its porous characteristics. However, the internal curing compensated for strength loss and lowered the chloride permeability. A lower water/binder ratio and incorporation of supplementary cementitious materials improved compressive strength and air void system quality, resulting in a lower total moisture uptake and chloride permeability due to the refined microstructure and reduced capillary connectivity. A modified penetration depth model was proposed to assess the frost resistance. When the calculated penetration depth surpassed the specimen thickness, the filling of water in the pore system caused severe frost scaling and degradation of the relative dynamic modulus. Freeze-thaw cycles also influenced the pore system of concrete in turn by increasing the size and continuity of capillary pores.

Long-life pavements are generally designed and built to last 30-50 years without major structural rehabilitation and reconstruction. They achieve their design service life with periodic surface renewal due to surface distresses. Recently, two long-life concrete pavement pilot sections were constructed in Michigan. This paper evaluated the design and construction enhancements employed to achieve longer lives. The long-life pavements differ from standard ones mainly for construction materials, that is, having a cement-stabilized permeable base and stabilized subgrade. Laboratory-determined mechanical properties of the concrete used in both projects surpassed their target. The base layer MR values are higher and lower for the subbase layer than their assumed values at the design stage. The as-designed and as-built predicted pavement performance showed that either design alternative would achieve its intended design lives; long-life pavements had a slower rate of progression of IRI and joint faulting. The LCCA comparison revealed that the long-life design pavements are more cost-effective considering the estimated total cost (i.e., agency and user costs).

The effectiveness of using pre-wetted lightweight aggregate (LWA) for internal curing was investigated based on a laboratory testing program with a primary objective to reduce or mitigate curing related shrinkage (i.e. autogenous), as this could pave the way for using LWA in concrete for repair projects such as bonded overlays or new construction (e.g. JPCP projects). A concern with the use of LWA is the high absorption coefficient and potential negative impact on freeze-thaw resistance. A laboratory study was developed to evaluate compressive strength and key durability properties, such as rapid chloride permeability, RCP, sorptivity, and freeze-thaw (F-T) resistance (i.e. combined resistance to internal cracking and surface scaling in the presence of a 3% salt solution on the surface during repeated F-T cycles). Concrete mix variables were LWA content (25% and 40%). A total of three air-entrained batches were produced. Total cementitious content was 390 kg/m3 (658 lb/yd3) with 30% slag cement. The major findings are: Autogenous shrinkage can be mitigated by using pre-wetted fine LWA at a 25% to 40% volume content of total fine aggregate. Excellent F-T resistance with respect to internal cracking and surface salt scaling was found for LWA contents of 25% or 40%. A silane surface treatment was found partially effective as surface scaling accelerates once a fully saturated pore condition occurs. This suggests that the hydrophobic treatment prevents pressure relief by air-voids and "surface-breathing".

AbstractA number of parameters can influence the fluidity of an ultrahigh-performance concrete (UHPC) mix and, hence, its viability for use in construction. These parameters include the carbon cont...

Salt scaling is a commonly observed durability issue in concrete exposed to a combined salt and frost attack. This damage is restricted to a very thin surface region causing the removal of mortar flakes. This study demonstrates the surface-swelling characteristics of different concrete mixes. Significant paste swelling of the embedded fine silica sand peripherally occurs around the coarse aggregate particles in concrete mixes having a high water/cement ratio or insufficient air entrainment. Localized scaling is observed in concrete mixes with a denser matrix. The severity of this phenomenon is related to the magnitude of cryogenic suction governed by the permeability of the paste. Surface scaling is proposed to be the generator of bulging stress due to confined expansion from ice growth.

High Performance concrete, HPC, in this context is defined as being resistant to freeze-thaw, F-T, exposure in the presence of deicer salt, as well as having low shrinkage and low permeability characteristics. These properties were evaluated experimentally for air-entrained, low water-cementitious (0.40) concrete containing slag cement at a 30% cementitious replacement level. The effectiveness of sand replacement levels of 0% and 25% by volume of pre-soaked lightweight aggregate (LWA) for autogenous shrinkage control was evaluated from unrestrained shrinkage tests. The effectiveness of surface application of a hydrophobic admixture in reducing water uptake during pre-saturation prior to freeze-thaw exposure was investigated as well. Internal curing was found to be effective in mitigating shrinkage while at the same time achieving excellent F-T resistance despite the addition of a highly porous LWA.

In this paper, a two-dimensional geometric model is developed to characterise the air-void system in hardened cement paste. This model consists of non-overlapping circular voids of different size classes randomly placed in the cementitious matrix of a specific size. The major output of this model is the distance of a specific void from its nearest neighbour (void–void spacing). The cumulative distribution function of the nearest void–void spacing fits well the Rosin–Rammler model, from which the probability distribution function is derived. The number and distribution of the voids is obtained from the chord length measurement based on the linear-traverse method. The effect of paste content and air-void saturation on the void spacing is investigated to illustrate gradual increase in void spacing with a higher paste content or the partial filling of air voids. This model is validated by the good correlation between the calculated spacing factor and the tensile strain capacity of concrete from length-change measurement.

This study investigates the effects of replacing a portion of Portland cement with slag cement (0%, 25%, 50% and 65% by mass) on the properties of plain ultra-high performance concrete (UHPC) mixes. It is observed that slag cement substantially enhances the flowability of the UHPC mixes and reduces the superplasticizer dosage. Mechanical properties are evaluated for mixes with similar air void characteristics, indicating that early age strength is reduced while there is more strength gain in the later age. This early age strength suppression is consistent with semi-adiabatic hydration heat evolution. The presence of slag cement reduces the maximum temperature rise. Linear deformation measurement on duplicate sealed specimens reveals four distinct stages for the shrinkage development and slag cement increases the shrinkage strain in the steady state, associated with the pozzolanic reaction. Simultaneous measurement of moisture uptake, mass loss and relative dynamic modulus of elasticity (RDM) on UHPC mixes for F-T durability shows that the cumulative moisture uptake and mass loss, when normalized with respect to the paste content, are almost negligible compared with a regular concrete mix. This reconciles the capillary suction dominated surface scaling mechanism. No internal bulk cracking is detected due to the dense matrix restricting the ingress of external moisture and the amount of freezable pore water.

Creep, as an intrinsic property of concrete material, will inevitably affect the performance of concrete pavement slabs in the field. However, the creep effect on the performances of concrete pavement slabs is far from being fully investigated. In this study, a test set-up is designed to measure the flexural creep of concrete beams exposed to both sealed and drying conditions. The measured flexural creep results are then modeled by the microprestress–solidification theory-based creep model which is incorporated into finite element analysis to evaluate numerically the creep effect on the moisture warping deformation, warping stress, and the total stress under traffic load in concrete slabs. Parameters including slab size, slab thickness, and subgrade modulus are considered. It is found that concrete creep has a significant effect on slab performance. Based on the measured creep properties in this study, the warping deformation of slabs can be reduced by 8–62%, and the warping stress and the total stress can be relaxed by at least 50%. Therefore, it is of importance to incorporate creep effect in analyzing warping deformation and stress generated in concrete pavement slabs. This study also provides a numerical methodology to the current performance evaluation of concrete slabs in the field.

Pumping effect is studied by means of bulk moisture uptake in low water-binder (w/b) ratio concrete mixes under freezing-thawing (F-T) exposure. The added absorption is clearly demonstrated under either water or salt exposure with no appreciable difference noted. Air void degassing and subsequent saturation accelerated by the pumping effect is shown to cause void infillings commonly observed in concrete pavement exposed to prevalent freezing weather and deicing procedures in winter. Measured moisture uptake at two different minimum temperatures (−10°C and −20°C) indicates equally significant absorption suggesting external moisture forced into the concrete interior upon freezing is a major pumping effect. Concurrent investigation on the cumulative mass loss and internal damage reveals the decoupling of salt scaling and internal frost damage governed by different mechanisms. This is enhanced by the silane and temperature effects on the mass loss and relative dynamic modulus (RDM) change. Silane treatment and a higher minimum temperature (−10°C) are found to create much less scaling attributed to the restricted ice growth. However, the hydrophobic effect is neutralized by the hydraulic pressure at instant freezing, which maintains the universal pore saturation in concrete and eventually causes cracking.

Assessing the stress development in concrete requires an appropriate tensile creep model which is capable of incorporating the effect of the field environment conditions. This study quantifies the effect of temperature variation on the very early-age stress developments in restrained concrete by adopting a modified microprestress-solidification (MPS) theory-based creep model. The MPS creep model is first calibrated and verified based on the measured direct tensile creep data under normal and high temperature histories, it is then used to predict the very early-age stress development of the fully restrained concrete specimens under variable temperature history since casting. The predicted results are in good agreement with the experimental results. The tensile stress in restrained specimens can be relaxed by 80 %–87% within the first three days since casting. The predicted stress exhibits an obvious deviation from the measured one if temperature effect is not considered. Therefore, it is of importance to consider the temperature effect on concrete creep when the temperature variation in concrete is significant, and MPS creep model is valid for tensile stress prediction in concrete at very early ages.

Ultra-high performance concrete (UHPC) is a new class of cementitious materials that have exceptional mechanical and durability characteristics. UHPC is commercially available. However, its cost for construction of highway structures is prohibitive. Based on an extensive testing program, a new family of non-proprietary UHPC materials with excellent characteristics in compression and tension, as well as exceptional resistance to freeze-thaw and chloride ion penetration were developed. The most cost effective of these deviates from traditional UHPC mixtures in that it uses a 50:50 mix of Portland Type I and Ground Granulated Blast-Furnace Slag (GGBS) as a binder, lacks any silica powder (inert filler) and requires no post-placement treatment. The use of GGBS improves the material’s ‘greenness’ making it a more sustainable cementitious product. Specifications for making the new UHPC were proposed. The developed UHPC blend was then used to conduct a comprehensive study on bond between UHPC and deformed steel bars to facilitate and enable future structural applications. Bond pull out tests showed the developed UHPC requires significantly reduced development lengths in order to attain steel bar yield compared to traditional concrete. Models to characterize the bond strength were proposed and a UHPC joint consisting of two pre-cast bridge deck elements was developed and tested at full scale. It was shown that a 6” (150 mm) joint made of the developed UHPC was sufficient to successfully transfer loading between the decks.

Freezing–thawing (F–T) exposure produces higher absorption in concrete than an isothermal condition. This work investigated the moisture absorption characteristics in different air-entrained concrete mixtures under two exposure conditions (water and a 3% salt solution) by simultaneously monitoring the weight change, mass loss and internal damage of 100 × 100 × 70 mm concrete blocks subjected to repetitive F–T cycles. The results indicate that permanent bulk moisture uptake is primarily a result of the accelerated saturation of poorly connected capillary pores, the slow filling of entrained air voids in concrete mixes with sufficient air entrainment, or the re-saturation of newly generated cracks in concrete with poor frost resistance. No detectable discrepancy was observed in moisture uptake between water and salt exposures, but the mass loss difference was found to be substantial. The measured bulk absorption is not a reliable predictor for salt frost scaling resistance, since it reflects the universal moisture condition in the specimen while scaling deterioration is dominated by the degree of saturation in a thin surface region.