Controlled Permeability Formwork Liner Research Articles

Effect of surface curing condition on the humidity field and moisture transfer in concrete

In order to study the influence mechanism of different curing methods on the humidity field and scientifically design the surface curing methods, the humidity field of C30, C50 and C80 concrete cured with plastic film (PF), controlled permeability formwork liner (CPFL) and moisture retention curing film (MRCF) was measured by the designed testing device. And the pore structure of cement paste in the surface area of concrete with different curing methods was analyzed by mercury intrusion pore test (MIP). The theoretical calculation model for concrete humidity field considering the influence of surface curing method was also established. The results show that: CPFL curing improves the compactness of the concrete surface area by eliminating excess water and gas, reducing the rate of water loss and humidity decrease during the later drying process. It is more effective for the low strength concrete; MRCF curing extends the humidity saturation period and improving the final humidity level. It is more effective for the high strength concrete; PF curing creates an almost absolute humidity environment to prevent the moisture transfer during the curing period; The established model can accurately describe the impact of three different curing methods on the humidity changes for different strength concretes. It can be used to quantitatively analyze the humidity changes of concrete under different curing and environmental conditions. This study systematically clarifies the effect mechanism of different types of surface curing methods on the humidity field of concrete for the first time. And it will provide theoretical support for the scientific selection of concrete curing methods and accurate prediction of humidity field.

Effects on structural light weight aggregate concrete cast using controlled permeable formwork liner

The porosity of the concrete surface has the greatest influence on the durability qualities of the concrete. The surface porosity of concrete can be lowered by lowering the water-to-cement ratio. The present study investigates the durability properties of structural light weight concrete using Sintered Fly Ash Lightweight Aggregate (SFLA) combined with Controlled Permeable Formwork (CPF) liners. The Structural Light Weight Concrete (SLWC) possesses a denser Interfacial Transition Zone (ITZ), internal curing effect, and absence of wall effect. By draining excess water and air bubbles near the surface, CPF liners improve the quality of the concrete surface. Various tests were conducted to measure water penetration depth, water absorption, surface resistivity, charges passed, rebound number, pulse velocity, and wear resistance. The experimental results show that the combination of CPF liners and SLWC produced excellent results and performance in terms of surface resistivity, water penetration, water absorption, charges passed, and wear resistance, in the range of 18, 55, 51, 86 and 13 % respectively. This study suggests that CPF liners enhance the surface of concrete and improve its durability by decreasing the water-cement ratio at the cover region, reducing porosity.

The effect of permeable formwork on durability and corrosion performance of concrete

The longevity of any reinforced concrete element is determined by the quality of the cover concrete. The only way for aggressive chemicals to get into the structural components and cause rebar corrosion and other types of damage is through the cover concrete. The controlled permeable formwork (CPF) liner is a unique approach for enhancing the quality of cover concrete. This liner permits surplus water and trapped air to escape while keeping the cement and fine particles in place on the concrete surface. Due to the modification, the water-cement (w/c) ratio is reduced, cement content is increased and surface porosity in the concrete cover zone is reduced. The influence of CPF liner on durability property and corrosion resistance of reinforced concrete was investigated in this study. Concrete samples were cast against a CPF liner and impermeable formwork (IMF) at three different water-cement ratios (0.47, 0.40, and 0.33). The rapid penetration of chloride, ingress of chloride, migration of chloride and accelerated corrosion were all examined at various ages. The results showed that CPF concretes exhibited good resistance to chloride ion intrusion of 46–56%. Furthermore, when casting of concrete is done with CPF liner, the time it takes for crack is 1.5 times longer than when concrete is cast against IMF.

Effect of Formwork Liner on Durability and Corrosion Characteristics of Self Compacting Concrete

Recent advancements in improving the quality of cover concrete opened a new pathway known as controlled permeable formwork (CPF). In CPF liner, the air and water molecules were trapped in the concrete/formwork interface to spill/drain from concrete surface, at the same time retaining smaller cement and other fine particles. This novel approach, lowers the porosity of concretes surface area thereby mutually tends to improve/enrich the cement content. Another key advantage of this CPF liner system is its tendency to lower the proportion of w/c ratio (water-to-cement). The present experimental research work intends to analysis the impact of CPF liner regarding factors such as durability, corrosive nature along with chloride ingress of self compacting concrete (SCC) (reinforced) sample. For experimentation, initially the castings of concrete samples were done in relation to CPF liner and impermeable formwork (IMF) samples. Followed by various tests at different operating stages to evaluate rapid chloride penetration, chloride regress, chloride migration and accelerated rebar corrosion. On experimentation it can therefore be summed up as, CPF concrete attained phenomenal ability towards Cl ion ingress by 52%–71%. Moreover, the results also indicated that time for concrete cracking in relation to CPF liner was increased to about 1.8 times in comparison with conventional IMF concrete.

Utilization of Iron Tailings Sand as an Environmentally Friendly Alternative to Natural River Sand in High-Strength Concrete: Shrinkage Characterization and Mitigation Strategies.

The increasing annual emissions of iron ore tailings have proved a great threat to the natural environment, and the shortage of natural river sand, as well as the pursuit of sustainable development materials, provides motivation to reuse iron ore tailings as a fine aggregate in concrete. Due to the significantly different properties of iron tailings sand compared with natural river sand—such as the higher density, higher content of limestone particles smaller than 75 μm and its rough and angular shape—concretes prepared with iron tailings sand show remarkably higher shrinkage. This study presents the shrinkage characterization and shrinkage-reducing efficiency of three different methods on iron tailings, sand concrete and river sand concrete. The internal humidity was also monitored to reveal the shrinkage-reducing mechanism. The obtained results indicated that the autogenous and total shrinkage of iron tailings sand concrete were 9.8% and 13.3% higher than the river sand concrete at the age of 90 d, respectively. The shrinkage reducing agent (SRA) was the most effective shrinkage reducing method for river sand concrete, while for iron tailings sand concrete, super absorbent polymer (SAP) and controlled permeable formwork liner (CPFL) it worked best on autogenous shrinkage and drying shrinkage, respectively. Furthermore, the shrinkage mitigation strategies worked earlier for the drying shrinkage behavior of iron tailings sand concrete, while no such condition could be found for autogenous shrinkage.

The effect of formwork liner on the service life of self-compacting concrete

The service life of any reinforced concrete is dependent upon the superior nature of concrete and its overall quality and excellence as a suitable cover material. Concrete acting as cover material is the only means by which destructive agents or other elements can access or infiltrate the structure resulting in corrosive damage to the rebar and causing other types of damage to occur. As a liner, the controlled permeable formwork (CPF) is an active technique that enhances concrete as a cover material. Moreover, this liner allows for air and water that is trapped inside to drain or spill out from the surface area of concrete whereas retaining small particles and cement. Accordingly, this not only minimises the porosity of the surface area of concrete, but it also helps towards improving or enriching the actual content. However, it also reduces the size and proportion of water to cement ratio (w/c). This paper aims to present the influence of CPF liner concerning the durability properties and the service life of reinforced/strengthened self-compacting concrete (SCC). To achieve this aim, concrete samples were cast in relation to the impermeable formwork (IMF) and CPF liner. A series of experimental tests were then conducted at different stages in order to examine accelerated rebar corrosion, rapid chloride penetration, chloride ingress, chloride diffusion. The findings from conducting the experimental investigations revealed that CPF concrete acquired excellent resistance against the ingress of chloride ions ranging between 54 and 75%. Furthermore, the results showed that the service life of self-compacting concrete cast against CPF liner was extended by around 1.5 times as compared to IMF concrete.

Influence of controlled permeable formwork liner on surface quality of self compacting concrete

The resilience of strengthened or reinforced concrete is dependent upon the superior nature of concrete and its overall quality and excellence as a suitable cover material. Concrete acting as cover material is the only means by which destructive agents or other elements can access or infiltrate the structure resulting in corrosive damage to the rebar and causing other types of damage to occur. As a liner, the controlled permeable formwork (CPF), is an active technique that enhances concrete as a cover material. Moreover, this liner allows for air and water that is trapped inside to drain or spill out from the concrete’s surface while retaining small particles and cement. Accordingly, this not only minimises the porosity of the surface area of concrete, but it also helps towards improving or enriching the actual content. However, it also reduces the size and proportion of water to cement ratio (w/c). This paper aims to present the influence of CPF liner concerning the resilience of surface quality properties of self compacting concrete (SCC). To achieve this aim, concrete samples were cast in relation to the impermeable formwork (IMF) and CPF liner. A series of experimental tests were then conducted at different stages in order to determine rebound number, dynamic hardness number, superficial Rockwell hardness number, wear resistance and abrasion resistance. The findings from conducting the experimental investigations revealed that CPF concrete acquired excellent resistance against the abrasion resistance ranging between 46% and 60%. Furthermore, the results showed that by the application of CPF liner, the cover concrete (thickness: 20 mm) turned harder, when compared to core concrete. The cover concrete (thickness: 15-mm) turned softer than core concrete in conventional cast concrete.

Study on the Mitigative Effect of Controlled Permeable Formwork (CPF) Liner on Early-Age Shrinkage of Box-Girder Concrete

Because of its high binder content and severe construction environment, early-age cracking is one of the most important threats to concrete used in continuous box-girder bridge structures. In this study, controlled permeable formwork (CPF) liner was used to mitigate the early-age shrinkage and reduce the early-age cracking risk of box-girder concrete. Early-age shrinkage was measured by a noncontact method and started at 30 min after adding mix water until 7 d. Internal relative moisture content and pore distribution tests were also carried out to reveal the working mechanism of CPF liner. The results show that covering the concrete surface with CPF liner decreased early-age shrinkage significantly. Under the temperature of 20°C and the relative humidity of 60%, two-surface-covering and three-surface-covering CPF liner on concrete decreased the shrinkage by 44% and 48%, respectively, at 7 d compared with concrete without CPF liner covered on it. The main reason is that CPF liner enhanced the internal relative moisture content and resulted in better performance of the surface concrete.

Relationship of hotness or coldness of mizaj based on Persian Medicine viewpoints, with paraclinic factors

The durability of concrete cast near the conventional formwork (steel or wood) is reduced because of higher water-cement (w/c) ratio as compared with the concrete present in the core of the member. Various controlled permeability formwork (CPF) liners absorb or drain out excess water near formwork, can reduce the increase in w/c ratio of concrete near the formwork. This paper presents a quantitative study showing improvement in the properties of near surface concrete (NSC) by the use of a commercially available CPF liner, and comparing the performance of more easily available and cheaper alternatives to CPF liner used. Two types of concrete mixes with identical w/c ratio but different water contents were used. Three specimens were made for each of the two types of concrete mix and one surface for each of the specimen was cast using one of the CPF liners among a commercially manufactured CPF, particle board, and gunny bag. Four tests: Rapid chloride permeability test, AgNO3 colorimetry test, initial surface absorption test and pull off test were performed to study durability properties of NSC. Study of physical appearance in terms of blowholes and grey area on the concrete surface using image processing is also presented in the paper. Though commercially manufactured CPF produces better surface than the particle board and gunny bag, the improvement in NSC properties by use of gunny bag is also noteworthy.

Enhancement in the quality of near surface concrete using some formwork liners

Abstract The durability of concrete cast near the conventional formwork (steel or wood) is reduced because of higher water-cement (w/c) ratio as compared with the concrete present in the core of the member. Various controlled permeability formwork (CPF) liners absorb or drain out excess water near formwork, can reduce the increase in w/c ratio of concrete near the formwork. This paper presents a quantitative study showing improvement in the properties of near surface concrete (NSC) by the use of a commercially available CPF liner, and comparing the performance of more easily available and cheaper alternatives to CPF liner used. Two types of concrete mixes with identical w/c ratio but different water contents were used. Three specimens were made for each of the two types of concrete mix and one surface for each of the specimen was cast using one of the CPF liners among a commercially manufactured CPF, particle board, and gunny bag. Four tests: Rapid chloride permeability test, AgNO3 colorimetry test, initial surface absorption test and pull off test were performed to study durability properties of NSC. Study of physical appearance in terms of blowholes and grey area on the concrete surface using image processing is also presented in the paper. Though commercially manufactured CPF produces better surface than the particle board and gunny bag, the improvement in NSC properties by use of gunny bag is also noteworthy.

The effect of controlled permeable formwork (CPF) liner on the surface quality of concretes

Surface quality of the concrete is important for the durability of reinforced concrete structures, because the cover stands at the forefront defending both mechanical damages and chemical deterioration. Controlled permeable formwork (CPF) liner is an innovative material used to improve the quality of the concrete in the cover region, by allowing the air bubbles and mix-water to drain out from the surface of concrete whilst retaining cement and other fine particles. The present experimental investigation was proposed to study the effect of CPF liner on the surface hardness and wear of concretes. Suitable size specimens were cast against CPF liner and (impermeable) steel formwork (IMF) and tested at various ages. The results revealed that the surface quality/hardness of CPF concretes enhanced by 14%–58%. Further, it was ascertained that due to CPF liner, 20 mm thick cover concrete was found to be harder than the core concrete. In conventionally cast concrete, 15 mm thick cover concrete was found to be softer than the core concrete. This change in the quality of cover concrete was found to be consistent over the w/c ratio of 0.31–0.48.

The effect of controlled permeable formwork liner on the mechanical and durability properties of self compacting concrete

The quality of the surface zone of concrete is a crucial factor for durable concrete structures, as it is the first line of resistance to penetration of aggressive agencies. Use of controlled permeable formwork (CPF) liner is one of the techniques employed to improve the quality of the surface zone of concrete. CPF liner drains mix water and entrapped air from the near surface of concrete while retaining cement and other fine particles. This helps to reduce water-cement ratio, increase cement content and decrease surface pores in the surface zone of concrete. It is postulated that CPF drains air and water, which migrate towards the formwork due to vibration caused while compacting concrete and hydrostatic pressure. In the present investigation, an experimental study was carried out to verify the performance and efficiency of CPF liner against self-compacting concrete (SCC). Suitable size specimens were prepared using impermeable formwork (IMF) and CPF liner as well. Tests were carried out to check compressive, split tensile strength and flexural strength; ultrasonic pulse velocity and rebound hammer; abrasion resistance, sorptivity and water absorption. The test results reveal that CPF liner performs equally well with SCC. Vibration/hydrostatic pressure may not play significant role in draining the interface water through CPF liner.

The effect of controlled permeable formwork liner on the mechanical properties of concrete

Controlled permeable formwork (CPF) liner was developed primarily to improve the surface quality of concrete and thereby its durability. CPF liner allows air and water to escape from the surface adjacent to the formwork. This paper reports an experimental study carried out to investigate the influence of CPF liner on the strength and certain mechanical properties of concrete with three different water–cement (w–c) ratios. The specimens were prepared against CPF liner and impermeable steel formwork (IMF) and tested at various ages starting from 7 to 365 days. Various tests were conducted to assess surface quality; compressive, split tensile and flexural strengths, rebound hammer and abrasion resistance of concrete. The results indicate that CPF concrete performed better than IMF concrete in all aspects. The present investigation reveals that the use of CPF liner has significantly improved the tensile strength (say, 20 %) of concrete and the abrasion resistance has been enhanced to a remarkable level (50–80 %). Further, the surface quality is very essential to assess the cube strength of concrete and the existing testing method slightly underestimates the cube strength.

Mould release technologies with regard to concrete surface finish

Concrete durability is in part dependent upon the quality of the concrete cover zone. The type of mould release technology used has a direct effect on the surface finish of fair-faced concrete, and this in turn affects long-term durability. This work examined two mould release agents (MRAs), one permeable formwork liner and a type 1 polypropylene fibre concrete combined with a single MRA. Cubes were cast in film-faced plywood moulds using C40 concrete that enabled comparisons to be drawn between the MRAs. The pilot study examined a range of variables for two different reactive MRAs (FS (petroleum based) and CL (vegetable oil based)). The release agents used are commercially available as reactive-based MRAs. In addition, controlled permeability formwork (CPF) and a concrete mix with polypropylene fibre additions were used. The pilot study results showed that the CPF liner produced the least number of blowholes and, in that respect, was the best performing technology used. Consequently, the CPF provided the most likely finish that would provide long-term durability. None of the technologies employed produced a completely uniform colour throughout, but the CL MRA cubes and polypropylene fibre reinforced cubes produced the most consistent colouring. Two of the best performing mould release products (CPF and FS) were then tested using a high-resolution optical measurement system and the initial results were examined in much greater detail, taking account of surface roughness, pore volume and pore size. The CPF proved to produce a better finish than the FS release agent.

Evaluation of Pore Size Distribution for Controlled Permeability Formwork Liner

Controlled permeability formwork liner (CPFL) is the functional material similar to nonwoven fabrics and its filtration and drainage performance is dominated by the pore size distribution (PSD) of matrix. In this paper, suction table method, generally used to measure soil pore diameter, is improved for testing PSD of CPFL and experimental data was compared to the results from four other normal experimental methods, i.e., wet sieving method, bubble point method, mercury intrusion porosimetry (MIP) method and image analysis. The comparison indicates that PSD of CPFL obtained from suction table show good accuracy and repeatability. Furthermore, a modified mathematical model derived from Rawal model and Fature model is proved to be suitable for determinating PSD of the matrix of CPFLwith bilayer structure, and have a good agreement with the experimental data from suction table.

Research on Controlled Permeability Formwork of Nonwoven Fabrics to Retain the Humidity on the Concrete Surface

It is of great significance for concrete to be cured using controlled permeability formwork of nonwoven fabrics especially in dry area. CPF can improve durability of concrete through decreasing the ratio of water and cement in concrete surface. CPF could also retain the water within it. The role of concrete curing using CPF or not is test by MOIST200B type microwave moisture meter. In addition, the permeability of concrete surface between the concrete which use CPF or not is analyzed through the air permeability test, the initial surface absorption of concrete test (ISAT). The testing results indicate that there is little effect on curing of concrete using controlled permeability formwork liner.

Effect and mechanism of controlled permeable formwork on concrete water adsorption

Controlled permeability formwork (CPF) is a kind of non-woven formwork, which is a widely used product in the spinning industry. In this paper, the effect of CPF on the water adsorption property of concrete was studied. Surface appearance, meso-surface morphology and microstructures of concrete blocks were characterized to analyze the affecting mechanism of CPF on concrete adsorption. It was found that, by applying CPF, concrete permeability was markedly reduced due to the improved surface and microstructures. In addition, the surface structure of the CPF liner was studied by SEM. It was indicated that the CPF was a beneficial and promising material for the improvement of concrete performances.

Multiscale Performance Characterization of Concrete Formed by Controlled Permeability Formwork Liner

It is well known that the permeation and retention of water with a controlled permeability formwork (CPF) liner directly contribute to discharging superfluous water and minimizing bubble content when fresh concrete is poured and cured. These phenomena considerably improve the properties of concrete. To comprehensively evaluate this technology, an extensive experimental program on evaluating the discharged water, moisture content, water-binder ratio variation during the casting process, and surface quality of specimens formed with the CPF liner and control formwork was conducted. Two types of CPF liners with different parameters in the vertical and horizontal permeability coefficients, weight, nominal thickness, and air permeability coefficient were considered. In addition, multiscale experimental characterization of concrete samples, including chloride ion permeability, abrasion resistance, ultrasonic test, scanning electron microscope, and mercury intrusion porosimetry, was performed. It demonstrated that the compactness, antipermeability, and rebound strength of specimens were increased effectively if the key parameters (e.g., permeability coefficients, weight, and thickness) of the CPF liner were properly chosen. Moreover, the fractal dimension of material porosity, which correlates to the cumulative volume of intruded mercury for the specimens, was computed, and it was capable of quantifying concrete surface densification and revealing the quality-improvement mechanism of concrete formed with the CPF liner.

Effects of Controlled Permeability Formwork on Surface Properties and early Age Shrinkage of Concrete

Concrete durability is one of the most important considerations in the design of new structures in aggressive environments. It generally depends on the quality of the concrete surface and the cracks of concrete. In this paper, the rebound numbers of concrete cast using controlled permeability formwork (CPF) and ordinary steel formwork were determined. And the early age shrinkages of concrete cured in dry environment of 20±2°C, 75±5% RH, in sealed condition with plastic film and in covered condition with CPF liner were measured. Testing results indicated that CPF could improve the concrete surface hardness and reduce the early age shrinkage of concrete. So CPF can enhance concrete durability and prolong its life-span.

The influence of reusing ‘Formtex’ controlled permeability formwork on strength and durability of concrete

The effects of the reuse of ‘Formtex’ Controlled Permeability Formwork (CPF) liner on strength and durability properties of concrete were investigated at two different water-cement ratios and the results are reported in this paper. Test blocks were cast using the CPF on one side and impermeable formwork (IF) on the opposite side of the mould so that direct comparisons could be made between the two. The strength was assessed using the Limpet pull-off tester and both the air permeability and the water absorption (sorptivity) were measured using the Autoclam Permeability System. Both these instruments measured the ‘covercrete’ properties. In addition, cores cut from the test specimens were subjected to an accelerated carbonation test and a chloride exposure test. The results showed that the ‘Formtex’ CPF increases the surface strength and the durability of concrete compared to the IF. There was an almost complete elimination of blowholes. The permeability of concrete decreased and its resistance to the ingress of both carbon dioxide and chlorides increased when CPF was used. The beneficial effects of the Formtex CPF were most evident in concrete of higher water-cement ratio. With the reuse of the Formtex liner twice, that is a total of three uses, the performance of the CPF to improve the properties of concrete remained almost the same. In this research the CPF liner was cleaned thoroughly between each use, which must be adhered to for site applications for reproducing the beneficial effects observed in the laboratory.