Reduction Of Autogenous Shrinkage Research Articles

Integration of monitoring indicators for self-sensing alkali activated cementitious materials: From electrical signals - resistivity to autogenous shrinkage

The chemical shrinkage and autogenous shrinkage of alkali-activated materials (AAMs) are usually more significant than that of ordinary Portland cement (OPC). Therefore, both searching for efficient methods to reduce shrinkage and exploring the shrinkage mechanism of AAMs are of great significance in promoting the application of AAMs. In this paper, metakaolin is used to reduce the chemical shrinkage and autogenous shrinkage of AAMs, while an innovative resistivity measurement is used to concretize the electrical signal of AAMs and the relationship between autogenous shrinkage and resistivity was explored. The early resistivity and heat of hydration curves of AAMs can be divided into five stages with high similarity, demonstrating the feasibility of indirectly quantifying the autogenous shrinkage and chemical shrinkage by resistivity. The results of TG-IR, MIP, and heat of hydration prove that the early reaction rate of AAMs decreases with the increase of metakaolin content, which further leads to the decrease of early chemical shrinkage and autogenous shrinkage. The reduction of autogenous shrinkage reached the maximum (49%) when the metakaolin content was 50%. A mathematical model between autogenous shrinkage and resistivity was established, which means that the resistivity of self-sensing materials can be used as an index to evaluate the early autogenous shrinkage of AAMs.

Mechanical and shrinkage performance of steel fiber reinforced high strength self-compacting lightweight concrete

This study investigated the effects of mixture proportion on the mechanical and shrinkage behaviors of steel fiber reinforced high strength self-compacting lightweight concrete (SHSLC) mixtures incorporating bottom ash aggregates for internal curing. In this study, different types of fine aggregates, fine aggregate ratios, supplementary materials such as silica fume (SF) and colloidal nano-silica (CNS), and four types of steel fibers were considered to develop SHSLC. The self-compacting characteristics of concrete were evaluated by means of slump flow, J-ring flow, and V-funnel tests. The test results indicate that incorporation of SF and CNS had a positive effect on the mechanical properties, but 4% incorporation of CNS decreased workability and strength due to the agglomeration of mixture. The addition of steel fibers improved compressive strength, and flexural toughness of SHSLC, but reduced the flowability and passing ability with increased fiber contents. Due to the internal curing from coarse bottom ash, significant reduction of autogenous shrinkage up to 33% was observed, whereas 7% for drying shrinkage. The incorporation of fibers reduced the autogenous and drying shrinkage up to 31% and 22% compared with non-fiber reinforced concrete, respectively. Finally, the autogenous shrinkage behavior was simulated with several models in the literature, and a model for high strength self-compacting lightweight concrete with and without fibers considering equivalent age was proposed.

Development of low-carbon and cost-effective ultra-high performance concrete using carbonated recycled fine aggregate

This paper studied the influence of carbonated recycled fine aggregate (RFA) on mechanical and microstructural performance of ultra-high performance concrete (UHPC), aiming to develop a low-carbon and cost-effective UHPC. This includes the changes in strength, hydration kinetics, RFA-to-paste interfacial microstructure, and pore structure with the use of carbonated RFA. The environmental and economic effect of using carbonated RFA in UHPC is evaluated. The RFA content was investigated at 0–30%, by mass of total sand. Experimental results showed that a reduction greater than 10% in crushing index and water absorption of RFA was achieved by carbonation. The increase of carbonated RFA content from 0 to 30% led to 45% reduction in autogenous shrinkage of UHPC. The use of 20% uncarbonated RFA resulted in 12% and 10% reduction in 28-d compressive and flexural strengths, respectively, while such use of carbonated RFA can secure similar 28-d compressive and flexural strengths compared to those without RFA. Despite the reduced cement hydration, the use of carbonated RFA can secure a denser RFA-to-paste interfacial microstructure and refine the pore structure of UHPC compared to those made with uncarbonated RFA, given the chemical bonding and nucleation effect of carbonated RFA. Moreover, the use of 20% carbonated RFA can enable 5% decrease in the Global Warming Potential value evaluated by life cycle assessment compared to that without RFA. Such use of RFA led to a decrease greater than 15% in UHPC cost. This indicated the low-carbon and cost-effective characteristics of the developed UHPC made with carbonated RFA.

Influences of high-volume coal bottom ash as cement and fine aggregate replacements on strength and heat evolution of eco-friendly high-strength concrete

This study investigates the potential of using high-volume bottom ash as a supplementary cementitious material (SCM) and fine aggregate replacement in production of high-strength concrete. In the first stage, bottom ash quality was improved by sieving through a No. 50 sieve and grinding to increase fineness. Ground bottom ash (GBA) replaced ordinary Portland cement (OPC) at 35%, 50%, and 65% by weight to produce high-strength concrete. In the second stage, coarse bottom ash (CBA) retained by a No. 50 sieve replaced fine aggregate in an optimum mixture at 20%, 40%, and 60% by volume. Concrete properties including compressive strength, modulus of elasticity, autogenous shrinkage, and heat evolution were evaluated. The economic and environmental impacts of GBA were assessed. The results indicated that concrete with 50% GBA cement replacement could be classified as high-strength concrete at 7 d, achieving a compressive strength of approximately 80.9 MPa at 28 d. Autogenous shrinkage was decreased with an increase in GBA content. The heat evolution of concrete with 50% GBA was decreased by 36.4% compared with the control concrete. Concrete with 50% GBA cement replacement and 60% CBA fine aggregate replacement demonstrated the greatest reduction in autogenous shrinkage and peak of heat evolution, and it was classified as high-strength concrete.

The Effect of Hydrogels with Different Chemical Compositions on the Behavior of Alkali-Activated Slag Pastes.

The effect of in-house synthesized hydrogels with different chemical compositions on the properties of alkali-activated slag pastes was examined. It was found that the teabag test and modified teabag test as a direct method and the flow test as an indirect method showed a similar trend in hydrogel absorption; however, the absorption values differ noticeably between the direct and indirect methods. The alkali-activated slag pastes with hydrogels demonstrated a significant reduction in autogenous shrinkage compared to the pastes without hydrogels. The creation of macrovoids by the hydrogels and change in pore structure resulted in a decrease in compressive strength and electrical resistivity of the pastes with hydrogels. The absorption and desorption of hydrogels in the pastes were tracked using X-ray microcomputed tomography (micro-CT), and it was shown that the onset of hydrogel desorption approximately coincided with the final setting time of the pastes.

Autogenous shrinkage reduction and strength improvement of ultra-high-strength concrete using belite-rich Portland cement

Autogenous shrinkage is a non-trivial problem affecting the use of ultra-high-strength concrete (UHSC). Hydration is an important cause of autogenous shrinkage. This study proposes a method to reduce autogenous shrinkage and increase strength by controlling the hydration reaction of the binder. Belite-rich Portland cement (BPC) was used to replace a fraction of the type I ordinary Portland cement (OPC) in the binder (replacement ratios of 33%, 66%, and 100%), and the hydration heat, autogenous shrinkage, compressive strength, hydration products, ultrasonic pulse velocity, electrical resistivity, and CO2 emissions were simultaneously determined. The results are summarized as follows: 1) With increasing BPC substitution ratio, the autogenous shrinkage of the specimen decreased because the addition of BPC lowered the hydration rate. 2) The addition of BPC reduced the early compressive strength (3 and 7 d) and promoted the development of long-term compressive strength (28 and 56 d). 3) The microstructural analysis showed that compared with the control group, the low reactivity of BPC leads to less Ca(OH)2, AFt, and AFm production. 4) The ultrasonic pulse velocity and strength had a strong linear relationship for various specimens at different ages. 5) The electrical resistivity gradually decreased as the amount of BPC substitution increased. 6) The addition of BPC reduced the normalized CO2 emissions per MPa of strength. In summary, upon replacing OPC with BPC, UHSC exhibited lower autogenous shrinkage, lower cumulative hydration heat, lower CO2 emissions, and higher long-term strength.

Influence of Fineness of Wheat Straw Ash on Autogenous Shrinkage and Mechanical Properties of Green Concrete

This study investigates the effectiveness of an agricultural by-product wheat straw ash (WSA) as an internal curing agent in reducing the autogenous shrinkage of high-performance concrete (HPC). After incineration under different controlled time–temperature conditions, grinding and sieving were performed to obtain two different grades of fine WSA (F-WSA) and superfine WSA (SF-WSA). Subsequently, material characterization tests were carried out, followed by tests for mechanical properties and autogenous shrinkage potential of concrete incorporating 10% and 20% F-WSA and SF-WSA as a partial replacement of cement. The results demonstrated slightly higher compressive and tensile strength of concrete containing SF-WSA compared to control, whereas concrete with F-WSA demonstrated comparable strength results to that of the control concrete. Moreover, a significant reduction in 7 days’ autogenous shrinkage was observed in concrete containing 10% and 20% F-WSA by 42% and 25% compared to that of control concrete, respectively. This reduction in autogenous shrinkage increased further to 57% and 40% for concrete with 10% and 20% SF-WSA, respectively. The results of microstructural investigations on paste samples such as FTIR, TGA, and N2 adsorption analyses revealed a more refined and compact microstructure of paste samples with increasing fineness of WSA due to the formation of a more densified C-S-H phase. The improvement of the microstructure is attributable to the improved pozzolanic properties of SF-WSA compared with F-WSA.

Effect of clay content on shrinkage of cementitious materials

Clay-like substances in manufactured sand significantly impact the shrinkage of cementitious materials. This study investigated the effect of clay content on autogenous shrinkage, drying shrinkage, hydration rate, internal relative humidity (IRH), elastic modulus and pore structure of cementitious materials. The water content and self-contraction of clay during desorption were also studied to clarify the underlying mechanism of its influence on shrinkage. The results indicate that the clay slightly alleviated the autogenous shrinkage while significantly aggravated the drying shrinkage. Pronounced self-contraction of clay occurred as RH dropped, but the conversion ratio of the self-contraction of clay to the shrinkage of mortar was very low. It is concluded that the self-contraction of clay obviously influences the pore structure and the evolution of the various performance of mortars. Furthermore, the initial swelling of clay and the gentle decline of IRH are account for the reduction in autogenous shrinkage. Meanwhile, the coarsened pore structure accelerates the drying shrinkage and the self-contraction of clay intensifies the drying shrinkage.

Microstructural behaviour and shrinkage properties of high-strength fiber-reinforced seawater sea-sand concrete

The use of seawater (SW) and dredged sea-sand (DSS) in concrete manufacturing could bring considerable environmental and economic benefits. However, due to lack of information on properties of the concrete made up of SW and sea-sand (SS), their application in industrial practice is rather limited. Shrinkage is an important property that affects concrete long-term strength and durability. To better understand and improve shrinkage performance, the behavior of high-strength fiber-reinforced seawater sea-sand (SWSS) concrete was investigated in this study. Polypropylene (PP) and polyvinyl alcohol (PVA) fibers with varying volume content (0.1% ∼ 0.5%) were used for concrete reinforcement. The autogenous and drying shrinkages of fiber reinforced SWSS concrete were examined and compared with those of the plain SWSS and freshwater natural sand (FWNS) concretes. The microstructural characteristics of the concrete mixes were also studied using various approaches including thermogravimetric analysis, X-ray diffraction analysis, nitrogen adsorption test and scanning electron microscopy images. Experimental results indicated that using SW and DSS resulted in an increase in the autogenous and drying shrinkage of the concrete due to existence of chloride, sodium, and potassium ions. These ions led to cement hydration acceleration, higher activation of ground granulated blast furnace slag and formation of C-A-S-H, consequently, a higher shrinkage value. Addition of either PP or PVA fibers could decrease the concrete shrinkage and a higher dosage of fibers caused a higher reduction in the shrinkage values. While both PP and PVA showed almost similar reduction in autogenous shrinkage, PP fibers resulted in a lower level of drying shrinkage. Compared with FWNS, lower cementitious hydration products (C-H and C-S-H) were observed in SWSS concrete. Effects of fibers on the hydration products were insignificant. Although SWSS concrete porosity was lower than that of conventional concrete at early-age, higher porosity was observed for SWSS after 63-days of curing. Finally, this study shows that the incorporation of fibers in SWSS concrete increased its long-term total porosity.

The Effect of Biochar on the Properties of Alkali-Activated Slag Pastes

This paper examines the influence of biochar on the properties of alkali-activated slag pastes using two activator solutions, namely NaOH and Na2CO3. The biochar demonstrated different absorption kinetics in the mixture of slag and the two activator solutions. The pastes with biochar showed a delay in the heat flow peak, compared to the pastes without biochar, but the cumulative heat release in these pastes at later hours was increased, compared to the pastes without biochar. It was found that the use of biochar reduced autogenous shrinkage in the pastes and the reduction in autogenous shrinkage was more pronounced in the alkali-activated slag with NaOH, compared to Na2CO3. The void structure of the pastes was investigated using x-ray micro-computed tomography. It was found that refined pore structure due to reduced effective solution/slag in the pastes with biochar was able to compensate for the decreasing effect of biochar voids on compressive strength. The electrical resistivity was shown to be lower in the pastes with biochar.

Internal curing of cement composites using kenaf cellulose microfibers

This study investigated the applicability of kenaf cellulose microfibers (CMFs) as an internal curing agent in cement composites. The test variables were the length and mass fraction of kenaf CMFs. Two types of CMFs, approximately 400 μ m and 5 mm long respectively, were prepared by pulverizing kenaf strand fibers. The amount of CMFs varied, at 0, 0.3, 0.6, 1, 2, and 3% of the cement by weight. The internal curing of cement composites was assessed by autogenous shrinkage and internal relative humidity tests. The internal curing effects were also examined by compressive strength testing and microstructural analyses, including thermogravimetry and microscopy. Regardless of the CMF type, the use of a higher CMF ratio caused a 12∼63% reduction in autogenous shrinkage and a 3∼30% increase in relative humidity. Of the two CMF types, the shorter CMFs were more effective in reducing autogenous shrinkage due to their better dispersion and restraining effect. In contrast, a better compensation for relative humidity resulted from the longer CMFs. Both types of CMFs were effective for internal curing, considering that the mixtures with CMFs generally exhibited a good correlation between rate of addition and increases in internal relative humidity and related reductions in autogenous shrinkage.

Mechanical performance and autogenous and drying shrinkage of MgO-based recycled aggregate high-performance concrete

The high strength and durability of high-performance concrete (HPC) may be significantly reduced by shrinkage cracking. The use of reactive magnesium oxide (MgO) can reduce shrinkage of cement-based materials due to its expansive properties. This study intends to analyse the validity of MgO as shrinkage-reducing agent in recycled aggregate HPC. To do so, ten HPC mixes with 0%, 25%, and 100% of both early-age (7-days air curing) and matured (6-month air curing) RA were produced. In half of the mixes, 10% ordinary Portland cement was replaced with MgO. The use of MgO slightly worsened the mechanical behaviour of HPC, especially when combined with large amounts of RA. On the other hand, the expansion of MgO fully offset the autogenous shrinkage of HPC and reduced total shrinkage by around 20–40%. Water storage of RA, and its deferred release over time, produced a more efficient hydration of MgO, which in turn led to a further reduction of autogenous shrinkage. However, the increase of drying shrinkage caused by RA was greater than this decrease of autogenous shrinkage due to MgO, so the higher the RA content of HPC the lower the total shrinkage reduction when adding MgO. Thus, the decrease of total shrinkage caused by MgO was compensated by the shrinkage increase because of RA when adding amounts above 35% early-age RA and 42% matured RA. Therefore, despite the suitability of MgO as shrinkage-reducing agent in recycled aggregate HPC, its effectiveness was reduced with increasing amounts of RA.

Effect of superabsorbent polymers and expansive additives on the shrinkage of alkali-activated slag

In this study, superabsorbent polymers (SAPs) and two expansive additives (a MgO-based expansion agent and gypsum) were studied to possibly mitigate the shrinkage of AAS (alkali-activated slag) systems. To this end, an experimental study was carried out to evaluate the effect of SAPs and the expansive additives on the setting time, compressive strength, autogenous shrinkage, and total shrinkage of AAS. SAPs prolonged the setting time of AAS and decreased the compressive strength, while the expansive additives shortened the setting time of AAS. When gypsum was used as an expansive additive, the shortest initial setting time of AAS was less than 10 min. SAPs have a significant effect in reducing the autogenous shrinkage of AAS, and a better result was achieved when used together with the MgO-based expansion agent as the SAPs promoted the consumption of MgO. The 1H low-field NMR results showed that when the SAPs and gypsum were used together, the absorption capacity of the SAPs decreased, and part of the absorbed liquid was rapidly released back into the mortar matrix. However, for the total shrinkage, the SAPs were less effective. SAPs increased the mass loss of the AAS mortar upon drying, which may increase the drying shrinkage of AAS and counteract part of the reduction in autogenous shrinkage.

Fresh and hardened properties of self-compacting concrete containing recycled fine clay brick aggregates

Clay brick is one of the major components of demolition waste, which is generally landfilled. Effective and new uses of recycled clay brick may provide sustainability benefits in terms of landfill reduction. Therefore, this research aims at applying Recycled fine clay brick aggregates (RFCBA) with sizes from 0.075 mm–4.75 mm to prepare Self-compacting concrete (SCC). The effects of RFCBA on fresh and hardened properties of SCC were investigated. Saturated surface dry RFCBA was used to replace Natural fine aggregate (NFA) with the percentage of 25%, 50%, 75% and 100%, respectively, in making the SCC mixes. Although experimental results showed that the flowability, passing ability, and segregation resistance of SCC containing RFCBA (RFCBA-SCC) decreased with the increasing RFCBA content, these properties still satisfy the criteria of SCC. The compressive strength, splitting strength, flexural strength, and elastic modulus of the RFCBA-SCC mixes decreased with an increase of RFCBA content. Due to their porous nature, recycled fine clay brick aggregates may also be a source of additional water for internal curing. The internal curing effect was confirmed by the mercury intrusion porosimetry, X-ray diffraction, and thermogravimetric analysis measurements. Moreover, a significant autogenous shrinkage reduction of SCC is achieved by using the RFCBA due to the release of additional water pre-stored in the RFCBA. Therefore, it can be concluded that the addition of RFCBA to SCC mixtures can provide additional practical benefits in the hardened state.

Investigating the Effect of CNTs on Early Age Hydration and Autogenous Shrinkage of Cement Composite

In this study, the effect of carbon nanotubes (CNTs) on the physical properties of cement composites was investigated. The mechanism of the change of autogenous shrinkage of CNTs-reinforced cement composites was also examined. In the experiments, ordinary Portland cement (OPC) and fly ash (FA) were used as binders, and 0.0, 0.1, 0.3, and 0.5% multi-walled CNTs (MWCNTs) were added to fabricate pastes. When the hydration heat was measured through isothermal calorimetry, it was found that CNTs accelerated the early age hydration of the pastes and that the hydration rate increased as the CNT content increased. The compressive strength was the highest when the CNT content was 0.1%. As the CNT content increased, the internal relative humidity (IRH) decreased and autogenous shrinkage showed a decreasing tendency. Through the analysis of the correlation between autogenous shrinkage and IRH, it was confirmed that the reduction in autogenous shrinkage due to the addition of CNTs resulted from the decrease in bulk strain.

Influence of Urena lobata Fibre Treatment on Mechanical Performance Development in Hybrid Urena lobata: Fibre/Gypsum Plaster Composites

Autogenous shrinkage is related to the chemistry and changes in the internal structure of the cement concrete paste on drying. This problem of drying shrinkage in early stages that occur without any moisture transfer to the surrounding environment has triggered the incorporation of fibres in the cement concrete matrix to fill the micropores and control cracking (autogenous shrinkage). This study aimed at investigating the potential use of Urena lobata (UL) fibre as microreinforcement in enhancing mechanical properties of hybrid UL-fibre/gypsum cement composites used for plasters. The fibre was harvested from the coastal region of Cameroon and treated with 0.06 M NaOH over different periods. Dispersion of treated fibre bundles in the composite (at Wt. % UL-fibre dosages of 0, 1.5, 2.5, and 3.5) was facilitated by blending with the cement paste which also helped to improve interfacial bonding between the fibre and the cement matrix. The moisture/water absorption and flexural properties within the hardened cement matrix were quantitatively assessed, and it was observed that the incorporation of treated fibre accelerated the hydration process. The test results showed an increment in compressive strength and reduction in autogenous shrinkage for the hybrid UL fibre/gypsum cement composites, while lower percentage additions (less than 2.5%) of untreated fibre appeared to have adverse effects on specimens. It was observed that properly dispersed (blended) treated UL fibres filled the fine pores in the cement matrix by providing an additional nucleation site that resulted in a denser microstructure, which in turn enhanced the strengths and limited the autogenous shrinkage.

Properties and hydration mechanism of cement pastes in presence of nano-ZnO

Nano-ZnO could delay the setting and the hardening of cement pastes but promote the later cement hydration, which made it an ideal inorganic retarder in cement based materials. In this research, properties and structures of fresh and hardened cement pastes containing nano-ZnO (CZ) were tested. Early hydration of CZ was greatly delayed and its early mechanical performances were decreased. However, the 28 days compressive strength of CZ with 0.1 wt% nano-ZnO was slightly higher than that of blank paste. Nano-ZnO was rapidly dissolved in alkaline environment to form the amorphous Zn(OH)2 in the early hydration stage, the deposition of Zn(OH)2 layer on the surface of clinker particles would block the early hydration. With the processing of cement hydration, as-formed Zn(OH)2 would be further reacted with Ca(OH)2 to generate intermediate Ca(Zn(OH)3)2·2H2O, which broke the Zn(OH)2 coatings and promoted the cement hydration in this period. In addition, the coarsening of capillary pores ranged from 5 nm to 50 nm in hardened CZ matrix was observed, which was presumed to be responsible for the autogenous shrinkage reduction of CZ pastes.

Mechanical properties and durability of high-performance concrete internally cured using lightweight aggregates

An experimental investigation was conducted to determine the effect of internal curing of natural lightweight aggregates (LWAs) on the shrinkage, mechanical properties, and durability of high-performance concrete (HPC). Conventional aggregates were partially substituted with prewetted coarse and fine LWA at dosages of 5, 10, and 20% by volume. The early age autogenous shrinkage and drying shrinkage of the HPC mixtures were monitored for up to 180 days. The investigated properties of the HPC mixtures included compressive strength, modulus of elasticity, and splitting tensile strength at 28 days, as well as rapid chloride permeability and water absorption. The results revealed that, at a replacement level of 20% for both coarse and fine aggregates, the reduction in autogenous shrinkage of the HPC mixtures was approximately 118% at 28 days and 65% at 18 days. Furthermore, the test results indicated that the autogenous shrinkage measured between 15 h and 7 days after casting was reduced by approximately 75%. Fine LWAs were more effective in reducing autogenous shrinkage than coarse LWAs. This was attributed to the small particles, which allowed a good distribution of the water-filled internal curing within the cement matrix. It was also found that using up to 20% LWA could modify the 28-day autogenous shrinkage of HPC by reducing the cube compressive strength up to 70 MPa as compared to 86 MPa for the control mixture. In addition, the obtained strength values of the concrete mixes were found to be within the acceptable range specified by the ACI standard to be categorized as HPC. The findings of the study revealed that the utilization of LWA is feasible as an internal curing method for decreasing the volume changes, particularly at the early ages, and for avoiding the formation of cracks in HPC.

The influence of fiber type and length on the cracking resistance, durability and pore structure of face slab concrete

• The drying and autogenous shrinkage reduction effect is greatest for PVA fiber. • The efficiency in improving the cracking resistance follows the order of PVA > PAN > PP. • PAN fibers produce a low porosity, a low hardened air content and a high impermeability. • Durability differences caused by fiber can be interpreted by the pore structure and air void. The crack resistance and durability of face slab concrete are two important factors determining the normal operation and safety of concrete face rockfill dams (CFRDs). This paper investigates the influence of polypropylene (PP), polyvinyl alcohol (PVA) and polyacrylonitrile (PAN) fiber with two lengths (10 mm and 20 mm) on workability, strength, shrinkage behavior, cracking resistance and durability performance of face slab concrete. Besides, the parameters of the pores at multi-scales were investigated by a linear traverse method and the mercury intrusion porosimetry (MIP), respectively. The results in this study demonstrate that: (1) the efficiency in reducing the shrinkage and in enhancing the cracking resistance of face slab concrete follows the order of PVA > PAN > PP. In addition, both the impermeability and frost resistance of concrete can be improved by adding fibers, the efficiency is in the sequence: PAN > PVA > PP and PVA > PAN > PP, respectively. (2) increasing fiber length from 10 mm to 20 mm reduces the shrinkage by about 5.1%−7.0%, enhances the tensile strength ( σ ) by about 7.9%−9.2% and declines the cracking temperature ( T c ) by about 5.6–6.5℃, all of which could significantly improve the cracking resistance. Moreover, the increase in fiber length improves the frost resistance, but increases the relative permeability coefficient ( K r) by about 28%−47%. (3) The correlation analyses reveal that, the addition of PAN fibers produces a lower porosity, a lower fraction of large capillary pores as well as a lower hardened air content than the PVA and PP fibers at 28 days, thereby resulting in better impermeability of concrete. PVA fiber enhanced concrete gives the smallest spacing factor and the largest total number of air voids among all the fiber enhanced concretes, thus exhibiting the best frost resistance.

Autogenous Shrinkage of Internally Cured Conventional, Latex-Modified, and Very High Early Strength Latex-Modified Concrete and Mortar

Abstract Internally cured concrete has been shown to help mitigate early-age cracking and to provide improved durability performance in concrete elements. The increased absorptive capacity of lightweight aggregates (LWA) facilitates delivery of moisture to concrete internally during the curing process. In this study, a range of concrete mortar mixtures representative of mortar contained in bridge deck and pavement concrete mixtures were batched and tested for autogenous shrinkage. Two significantly different LWAs were utilized in this study: one LWA with an absorption typical of most manufactured LWA and one with a relatively low absorption for a manufactured LWA. Autogenous shrinkage test results clearly demonstrated the impact of use of prewetted LWA for internal curing. Reductions in autogenous strain ranged from 30 to 56 % depending on the type of LWA used as well as the percentage replacement of prewetted LWA for normal-weight fine aggregate. The reduction in autogenous shrinkage correlated with LWA replacement rate, and shrinkage was even further reduced for mixtures that included fly ash. Findings indicated that the lower-absorption LWA provides internal curing benefits when used at suitable replacement levels, which may exceed those currently specified by some state highway agencies. Use of the approach to computing LWA substitution rate provided in ACI (308-213)R-13, Report on Internally Cured Concrete Using Prewetted Absorptive Lightweight Aggregate, should provide adequate moisture delivery to support reduction in autogenous shrinkage and internal curing benefits and is suitable for proportioning of both the typical and lower absorption LWA to support internal curing. In addition to reduced autogenous shrinkage, use of prewetted LWA in very high early strength latex-modified concrete mixtures provided workability and work-time advantages.