Shrinkage-compensating Concrete Research Articles

Heat of Hydration Analysis and Temperature Field Distribution Study for Super-Long Mass Concrete

In this study, the combination of ordinary cement concrete (OCC) and shrinkage-compensating concrete (SCC) was utilized to pour super-long mass concrete. The temperature and strain of the concrete were continuously monitored and managed actively after pouring. The investigation focused on the temporal and spatial distribution patterns of the temperature field, the temperature difference between the core and surface, and the strain evolution. Based on the constructed hydration exothermic model of layered poured concrete, the effects of the SCC, molding temperature, and surface heat transfer coefficient on the temperature field were analyzed. The results show that the temperature of super-long mass concrete rises quickly but falls slowly. SCC exhibits higher total hydration heat than OCC. The temperature field is symmetric along the length but asymmetric along the thickness due to varying efficiency of heat dissipation between the upper and lower parts of the concrete. After final setting of the concrete, the strain varies opposite to the temperature and peaks at −278 με. A few short cracks are observed on the end of the upper surface. Moreover, the numerical simulation results are in good agreement with the measured results. Increasing the molding temperature and surface wind speed increases the temperature difference between the core and surface. Conversely, increasing the thickness of the insulation layer is an effective way to curtail this difference. Thermal stress analysis is carried out and shows that lowering the molding temperature of SCC and increasing the thickness of insulation material can effectively reduce thermal stress.

Monitoring the effect of MgO expansive additive on micromechanical properties of cementitious materials using a combined method of EDS-nanoindentation

The effect of MgO expansive additive (MEA) on micromechanical properties is significant for understanding both the expansive and the mechanical behavior of the shrinkage-compensating concrete containing MEA. This study monitored the stiffness of different phases appearing in the shrinkage-compensating cementitious material containing MEA by using a combined method of energy dispersive X-ray spectroscopy (EDS)-nanoindentation. The effect of MEA and hydration time on the calcium silicate hydrates (C-S-H) and portlandite was focused. The MEA weakened the micromechanical properties of C-S-H and portlandite mainly at early ages. Hydration is the main reason responsible for the elastic properties evolution of C-S-H. With a two-step homogenization scheme, the experimentally determined micromechanical properties of individual phases were successfully upscaled to the macroscopic elastic modulus of the material. This study is a pioneering study on uncovering the micromechanical signature of the shrinkage-compensating concrete containing MEA.

Experimental Investigation on Shear Behavior of the Interface between Early-Strength Self-Compacting Shrinkage-Compensating High-Performance Concrete and Ordinary Concrete Substrate.

To improve interface bonding stress, early-strength self-compacting shrinkage-compensating high-performance concrete (ESS-HPC) was selected as an excellent strengthening material to investigate by direct shear test. Tests on seventeen Z-type specimens were carried out considering the ESS-HPC and ordinary concrete substrate (OCS) compressive strength grade, the ESS-HPC curing age, the OCS surface roughness, and the ratio of steel shear dowels as the variables. A bond stress–slip model of the interface was proposed via statistical fitting. The results show that the surface roughness and ratios of steel shear dowels had the most important influence on the shear bond stress. The shear bond stress of the specimens without steel shear dowels increased by almost 15% as the ESS-HPC strength grade changed from C60 to C75. With the increase in the curing age, the shear bond stress showed a changing trend of first increasing and then decreasing. The coarser surface with the drilling method can improve the shear bond stress by 89%. To achieve a secondary increase in the shear bond stress of specimens with steel shear dowels, the minimum ratio of steel shear dowels was 0.83%. Analytical equations are proposed in combination with the CEB-FIB Model 2010 and AASHTO Model. The calculated results show reasonable agreement with the experimental results within an acceptable range.

Bond characteristics between conventional concrete and six high-performance patching materials

Repair of damaged concrete structures with patching materials is required for a wide variety of bridge and building applications. Despite the capabilities of conventional patching materials in replacing the spalled concrete, they are often unable to restore the original structural capacity. This has motivated research investigations to develop high-performance patching materials that can help damaged concrete structures regain their strength and durability characteristics. Such characteristics, however, are not properly achieved without a satisfactory bond between the concrete substrate and the patching material applied. To investigate this critical aspect, six high-performance patching materials, i.e., proprietary and nonproprietary ultra-high performance concrete, polypropylene and alkali-resistant glass fiber-reinforced concrete, high-early strength concrete, and shrinkage-compensating cement concrete, were systematically investigated and compared in the current study. The conducted experiments included a holistic set of splitting tensile and slant shear tests performed on the samples prepared with various surface roughnesses. The experimental test results provided firsthand information about the bond characteristics between normal-strength concrete and six high-performance patching materials. With the determination of corresponding adhesion and friction coefficient factors, the outcome of this study facilitates the selection and use of high-performance patching materials, depending on the availability of materials and repair needs.

Synergistic effects of ettringite-based expansive agent and polypropylene fiber on early-age anti-shrinkage and anti-cracking properties of mortars

Effects of the ettringite-based expansive agent (EA) and polypropylene (PP) fiber on early-age anti-shrinkage and anti-cracking behaviors of mortar are comprehensively investigated in this paper. Combined with mercury intrusion porosimetry (MIP) and scanning electron microscope (SEM) analyses, its mechanism of the combination of EA and PP fiber on shrinkage and cracking restriction behavior of mortars is also proposed. The results indicate that the drying shrinkage resistance and cracking resistance behavior of the specimens with the combination of EA and PP fiber, are better than those of the specimens with single EA and PP fiber, while their residual expansion strain in autogenous shrinkage is lower than that of the specimens with single EA. The results of MIP and SEM analyses confirm that the formation of self-compressive stress generated by reinforcing effects of PP fiber and well three-dimensional network structure of ettringite distribution during expansion stage will partly offset the shrinkage force during shrinkage stage. Therefore, the combination of EA and PP fiber is prone to create a non-cracking shrinkage-compensating concrete in real construction.

Influence of exposure conditions on expansion characteristics of lime-rich calcium sulfoaluminate-belite blended cement

Expansive characteristics of calcium sulfoaluminate-belite (CSAB) cement can be harnessed for making shrinkage-compensating concrete. The level of expansion is dependent on several factors, such as the amounts of ye'elimite and calcium sulfate available in CSAB cement. Moreover, calcium sulfate from an external source can also influence the expansion characteristics by increasing the supersaturation with respect to ettringite. In this study, the influence of externally available calcium sulfate was investigated by curing a blend of Portland cement (PC) and CSAB cement to different concentrations (1 g/l and 5 g/l) of gypsum solutions. Expansion of the PC-CSAB blended cement was found to be directly affected by the ye'elimite content (CSAB dosage) and the gypsum concentration in exposure solution. The presence of external calcium sulfate during the hydration of ye'elimite was found to affect the hydrate phase assemblage, the pore structure, and the morphology of ettringite. Furthermore, the level of expansion depended on the age at which the specimens were exposed to the gypsum solution, indicating the influence of matrix stiffness on resultant expansion.

Longitudinal box-beam bridge joints under monotonic and cyclic loads

Longitudinal joints used for connecting box beams in bridge superstructures are prone to the formation and propagation of cracks, causing various structural performance issues and durability concerns. Among possible solutions, the use of shrinkage-compensating cement concrete along with joint reinforcement has been investigated in the current study through full-scale experimental tests and supporting numerical simulations. The shrinkage-compensating cement concrete offered the capability of producing controlled compressive stresses during the early stage of hydration, counteracting detrimental tensile stresses that originate from the shrinkage of concrete. Longitudinal and transverse reinforcements were also included in the joint to ensure the proper transfer of forces. The response of the full setup was evaluated under five million load cycles, including various loading protocols and boundary conditions. The measurements recorded from the experiments consisted of strains and deflections at critical locations. To expand the scope of this investigation and understand the effect of interfacial bond strength and joint reinforcement, a set of numerical simulations were also performed. Through a new combination of concrete mixture and reinforcement detail, this study provided a holistic strategy to resolve the long-standing issue of degradation of longitudinal joints in box-beam bridges.

Effect of expansive agents on the workability, crack resistance and durability of shrinkage-compensating concrete with low contents of fibers

The effect of hybrid CaO- and ettringite-based expansive agents (HCSA) on the mechanical properties and durability of shrinkage-compensating concrete (SHRCC) is not well established. In this paper, SHRCC specimens were prepared incorporating with a high-performance calcium sulfoaluminate- hydrate calcium hydroxide expansive agent (HCSA) and three different types of fibers, i.e., polypropylene fiber (PP), polyvinyl alcohol fiber (PVA), and cellulose fiber (CF). The first part of the experimental program included material tests of the slump, compressive strength, restrained expansion ratio, early crack resistance, permeability and chloride penetration of SHRCC. The test results indicated that the HCSA-based SHRCC exhibited good workability, early crack resistance and durability. It is suggested that HCSA with a dosage of 7% − 8% of the weight of binder materials provided favorable shrinkage compensation and early crack resistance and had negligible impacts on the slump and compressive strength of the SHRCC. Although the content was low (approximately 0.7% by volume), PP fibers effectively improved the early crack resistance of the SHRCC. Adequate moist curing was also required to retain acceptable permeability and chloride penetration of the SHRCC. The second part of the experimental program involved tests on small-scale concrete basement slabs, which verified the effects of the expansive agent and fibers on the crack resistance of SHRCC at the component level.

Reinforcement corrosion and transport of water and chloride ions in shrinkage-compensating cement concretes

The transport properties obtained from the accelerated tests on the concrete mixtures that contain shrinkage-compensating cement have indicated that addressing the issue of shrinkage may come with the expense of increased permeability. This raised a fundamental question concerning the long-term durability of reinforced concrete structures made with this type of cement. In the absence of similar studies, a comprehensive experimental testing program was devised in the current study to understand the vulnerability of steel bars embedded in shrinkage-compensating cement concretes exposed to corrosive environments. This included a long-term corrosion monitoring of reinforced concrete specimens made with different dosages of shrinkage-compensating cement. In addition to finding the corrosion rate of embedded steel bars, air permeability, capillary absorption, and chloride diffusion tests were conducted to determine the transport properties of the concretes made with this type of cement. The experimental test results were then further supported and explained using mercury intrusion porosimetry analyses.

Chloride penetration in shrinkage-compensating cement concretes

Shrinkage-compensating cement (a.k.a., Type K expansive agent) is a calcium sulfoaluminate cement with the ability of providing volume expansion during early age, primarily due to the formation of ettringite. Despite the past studies on the strength, shrinkage, and hydration of shrinkage-compensating cement concretes, there was no systematic investigation to understand the performance of this type of concrete under exposure to aggressive agents, particularly chloride ions. To address this gap, a holistic testing program was established in this study to evaluate the strength, dimensional stability, and transport properties of concretes made with various dosages of Type K expansive agent. This included compressive strength, drying shrinkage, rapid chloride penetration, electrical resistivity, rapid chloride migration, and absorption tests. Both helium and mercury intrusion porosimetry analyses were also performed to further explain the experimental test results with the findings related to the distribution of pores. The results of this study confirmed the benefits of using Type K expansive agent (up to a certain dosage) in terms of increased compressive strength and reduced drying shrinkage. However, it was revealed that the permeability of concretes made with this type of cement is adversely affected. This issue was addressed by the identification of optimal dosages of supplementary cementitious materials, including fly ash and silica fume. Upon completing the necessary experiments on the improved mixtures, this study reported how low-shrinkage concretes with low susceptibility to chloride penetration can be developed with the promise of application in a wide variety of civil infrastructures exposed to harsh environmental conditions.

Experimental Study on Freezing and Thawing Cycles of Shrinkage-Compensating Concrete with Double Expansive Agents.

The freezing and thawing of construction concrete is becoming an increasingly important structural challenge. In this study, a shrinkage-compensating concrete based on a double expansive admixture was developed and its frost resistance was assessed through rapid freezing and thawing cycling. The frost resistance of the concrete was derived through the measurement and calculation of the relative dynamic modulus of elasticity (RDME) and the mass loss rate (MLR), and the freezing- and thawing-cycle microstructures and products of concretes with different expansive agents were analyzed using scanning electron microscopy (SEM). It was shown that changes in the properties of the concrete under freezing and thawing could be divided into three stages: slow-damage stage, fast-damage stage, and stable stage. Compared to concrete without an expansive agent, a single-expansive-agent concrete demonstrated excellent frost resistance during the slow-damage stage, but the frost resistance rapidly decreased during the fast-damage age. After 150 cycles (the stable-damage stage), the concrete with a U-type expansive agent (UEA): MgO expansive agent (MEA) mix proportion of 2:1 had the best frost resistance, with RDME and MLR values 17.35% higher and 25.1% lower respectively, than that of an expansive-agent-free concrete. These test results provide a basis for the study of frost resistance in large-scale hydraulic concrete structures.

Early-age performance of longitudinal bridge joints made with shrinkage-compensating cement concrete

Longitudinal joints that connect adjacent box beams in bridges are known to experience early-age cracks due to temperature and shrinkage effects. Such cracks can open a direct path for water and deleterious agents to penetrate into the bridge, causing corrosion of embedded steel rebars and degradation of superstructure and substructure elements. To mitigate this problem, a solution explored in this study is to use Type K shrinkage-compensating cement, which has the promise to enhance the volume stability of concrete, minimize early-age cracks, and thus, increase the service life of the entire structure. For achieving a holistic assessment of this solution, a test setup consisting of two full-scale box beams connected with concrete made with Type K shrinkage-compensating cement was investigated in the laboratory setting under various temperature profiles. Response data, including temperature, longitudinal and transverse strain/stress, and deflection, were collected at the joint and each box beam during the thermal tests. To extend the scope of investigations beyond the temperature profiles tested in the laboratory, a set of three-dimensional finite-element simulations were performed as well. The results obtained from both experimental tests and numerical analyses showed that the stresses in the joint made with shrinkage-compensating cement concrete remain below the cracking threshold under temperature and shrinkage effects. With maintaining a proper bond with the box beams, the developed joint was found to provide superior performance, especially at early age, addressing the issues associated with the use of conventional concrete in longitudinal bridge joints.

Developing Large Slab Airport Runways for the Next Century

The purpose of this research was to determine whether shrinkage-compensating concrete (SCC) made with Type K cement can create durable airport runways with fewer joints and reduced maintenance costs. The primary criterion examined was the ability of SCC to offset the effects of early-age drying shrinkage when the concrete is acted upon by external restraint. The interaction of restraint with SCC is important because restraint resists the expansive behavior that provides shrinkage compensation. Four sets of experiments were conducted, with increasing levels of Type K expansive mineral additive in each set. A set of test specimens consisted of four-inch diameter restrained columns. Each set consisted of three columns with varying degrees of stiffness in the restraint frame, including low, medium, and high-restraint stiffness. The medium-restraint column provides the theoretical response of new pavement cast against a mature slab, whereas the other two bracket the problem. The column specimens were instrumented using vibrating wire strain gages, which were embedded in the concrete, and load cells, which were affixed to the top of the columns. This research concludes that SCC can be effective even with a stiff boundary condition, and that SCC provides the potential for much longer-lasting airport runway slabs, as a result of reduced shrinkage and therefore fewer cracks.

CSA-based Portland-free binders to manufacture sustainable concretes for jointless slabs on ground

The paper is aimed to the evaluation of the influence of water/binder ratio, tartaric acid dosage and curing condition on rheological, elastic and physical properties of sustainable shrinkage-compensating concretes manufactured with calcium sulphoaluminate cement (CSA), anhydrite (CS¯) and supplementary cementitious materials (SCMs)/lime (CH) compound in place of ordinary Portland cement (OPC). Results indicated that tartaric acid-based set-retarding admixture governs the behavior of concrete both in fresh and hardened state. In addition, according to Abram’s model, results evidenced the water/binder ratio as a key factor in strength gain. Moreover, tartaric acid allows the production of shrinkage-compensating Portland-free concretes particularly indicated for slabs on ground. Finally, by replacing OPC with SCMs and lime, it is possible to obtain, both for CO2-emissions and energy consumption, a reduction up to 60% at equal strength class respect to an OPC-based concrete.

Effect of Dolomite as Expansive Agent and Shrinkage Reducing Admixture in Self-Compacting Shrinkage – Compensating Concrete

The principle of using expansive agents has been recommended to manufacture shrinkage compensating concrete provided that an adequate wet curing is carried out. On the other hand, shrinkage-reducing admixture (SRA) in the concrete mixes, has been more recently suggested to reduce the risk of cracking in concrete structures caused by drying shrinkage.
 This paper is devoted to the study of the influence of complex modifier in the form of superplasticizer, shrinkage reducing admixture and expansive agent CaO- MgO-based on the fresh properties, hardening processand restrained shrinkage of Self-Compacting-Shrinkage-Compensating Concretes. The combined addition of shrinkage-reducing admixture with expansive agent has been found to be successful in producing shrinkage-compensating concrete. It should be noted also that the shrinkage reducing admixture slightly improve the workabilityof the fresh concrete mixtures but, it slightly reduces the early compressive strength of concrete.

Characterization tools for shrinkage-compensating repair materials

Achievement of dimensional compatibility is one of the most important considerations in order to consistently achieve lasting repair works that do not undergo harmful cracking. Drying shrinkage of Portland cement concrete is generally inevitable and, although its magnitude can be reduced by optimizing or modifying the composition parameters, it remains significantly larger than its ultimate tensile strain. Conversely, the use of shrinkage-compensating concrete (ShCC) may allow to achieve a zero-dimensional balance with respect to drying shrinkage, through the use of a mineral expansive agent. The experimental work carried out in recent years at Laval University to evaluate the potential of shrinkage-compensating concretes (ShCC) for use as repair materials has in fact yielded quite promising results. Nevertheless, more research is required to turn ShCC systems into a truly dependable and versatile repair option. Among the issues still unresolved, suitable tests methods must be developed, not only to better characterize ShCC, but also to guide the specifications and perform field quality control. Efforts have thus been devoted to adapt or develop test procedures intended to better capture the particular volume change behavior of ShCC’s. The paper presents two test procedures intended to assess the shrinkage-compensating potential and the effective strain balance of ShCC in restrained conditions.

Preparation of Shrinkage Compensating Concrete with HCSA Expansive Agent

Shrinkage compensating concrete (SCC) has become one of the best effective methods of preventing and reducing concrete cracking. SCC is prepared by HCSA high performance expansive agent for concrete which restrained expansion rate is optimized by 0.057%. Slump, compressive strength, restrained expansion rate and cracking resistance test were carried out on SCC. The results show that the initial slump of fresh SCC was about 220mm-230mm, while slump after 2 hours was 180mm-200mm. The restrained expansion rate of SCC increased with the mixing amount of expansive agent. After cured in water for 14 days, the restrained expansion rate of C35 and C40 SCC were 0.020%-0.032%. With the dosage of expansive agent increasing, restrained expansion rate of SCC increased, maximum compressive stress and cracking stress improved, cracking temperature fell, thus cracking resistance got effectively improvement.

Experimental Study on Shrinkage-compensating Concrete with CaO-based Expansive Agent

In this study, shrinkage-compensating concrete mixtures were prepared with various amount of CaO-based expansion agent to investigate their workability, mechanical property and durability. The experimental results indicate that CaO-based Expansive Agent has little effect on the performance of the fresh concrete workability. The mechanical properties and durability have been affected by the boundary limitation conditions. Adding 20-25kg CaO-based expansive agent per cubic meter concrete in replacement of equal amount of cementitious materials or sand would effectively compensate the deformation induced by chemical shrinkage and drying shrinkage.

Evaluation of time-dependent strain loss in CFRP eccentrically reinforced Shrinkage Compensating Concrete (SHCC) flexural members

Eccentrically CFRP enclosed Shrinkage Compensating Concrete (SHCC) flexural members show benefits of easy prestressing, better durability and self-made camber compared with traditional prestressed concrete. This paper presents the experimental and analytical work to evaluate the expansion strain losses in the proposed flexural members. A proposed analytical model to calculate the time-dependent strain losses is established including variables of shrinkage and creep of SHCC concrete based on GL2000 model. The relationship between maximum expansion strain and axial stiffness of FRP (EA) is also constructed. The same procedure was also conducted for Portland Cement Concrete (PCC) for the CFRP-PCC beam specimens. It is indicated that the proposed analytical model produces an accurate prediction in strain losses over time.

Damage analysis of concrete members containing expansive agent by mechanical and acoustic methods

Abstract Shrinkage compensating concrete (SCC) and Self-stressing concrete (SSC) technique have been employed for reducing early-age cracking and leakage while the addition of expansive agent would have a negative impact on mechanical properties and durability. The objective of the current research was to quantitatively assess the damage development in cementitious materials with expansive agent by both the strength tests and nondestructive acoustic tests including ultrasonic measurements and acoustic emission (AE) tests. The damage degree was defined based on strength as well as ultrasonic properties and a significant linear relationship was observed between the damage degree and autogenous strains. AE parameters such as AE amplitude, AE counts and AE energy were related to AE activity of the cement-expansive agent system. Crack mode identification was performed based on the relationship between average frequency and RA value (rise time/amplitude). A decreasing ratio of tensile cracks and an increasing ratio of shear cracks were observed which could be an indication of aggravated damage inside the materials.