Controlled Permeable Formwork Research Articles

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.

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

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

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.

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.

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.

Effect of controlled permeable formwork on the improvement of concrete performances

In order to investigate the influence of controlled permeable formworks (CPF) on concrete, samples were made in steel modulus with and without CPF. Visible surface morphology, adsorption of water and chloride, permeability of Cl-, together with pore structure of the surface layers were studied and analyzed. It's indicated that, by the application of CPF, concrete could be enhanced and the surface is homogeneous without any visible blow-holes. Also, adsorption and permeability of water and chloride ion into concrete were inhibited. According to mercury intrusion porosimeter, the porosity in the thickness of 0-3mm under surface was reduced from 10.48% of the control sample to 7.04%. The largest decrease existed in pores with diameter of larger than 0.2μm. The study indicates that CPF could markedly improve the appearance as well as the durability of concrete structures.

Study on the thermal stability of Controlled Permeability Formwork

In this study, the thermal properties of a kind of new geotextile materials, so called controlled permeable formwork (CPF), were studied. Thermo-gravimetric analysis showed that the weight of CPF didn’t change much between 0~350 °C. Dynamic mechanical analysis showed that the storage modulus of CPF reduced from 25 MPa to around 10 MPa when the temperature rose to above 100 °C. The strength of sample decreased slightly with the increase of the temperature. The breaking elongation changed slightly with a maximum at 80 °C. The CPF showed excellent thermal stability and was suitable for general use in construction work.

An investigation into factors affecting the performance of composite controlled permeable formwork liners: Part II – Filter medium

The aim of the filter medium study was to determine the influence that various filter fabrics, fixing methods and reciprocal usage have on the efficiency of air and excess mix water removal from CPF cast concrete. The goal is to significantly reduce the water/cement (w/c) ratio at the near surface of the slab so that specific surface performance characteristics could be monitored. A general factorial was used for the design of experiments with the results being statistically analysed using a one and two-way ANOVA and interaction plots. A range of tests including permeability, surface quality, surface hardness, surface strength and ISAT are used to determine the effectiveness of each system. Results are compared to a control sample which was cast against impermeable plywood formwork. The textiles were developed around pore size guidelines which were determined through a particle size distribution study for EN 197-1 cement (CEM). The influence of the textile permeability with reciprocal usage was a dominant factor in affecting near surface performance properties of the cast slabs. Surface hardness, surface tensile strength and absorptivity were shown to increase by various amounts depending upon the factors involved. It was concluded that an effective CPF liner can be constructed from a glued or stapled PP, PE or N6 filter medium with no drainage medium present. However, longevity of the system and optimum surface characteristics were found using a PE textile specifically.

Evaluation of concrete mixes and mineral additions when used with controlled permeable formwork (CPF)

The influence of concrete mixes and commonly used mineral additions and their effects on the near surface performance of vertically cast concrete against controlled permeable formwork (CPF) are the focus of this study. Three grades of concrete (C25, C30 and C45) and mineral additives including GGBS and PFA have been tested for surface performance in situ with CPF. The various loadings were chosen to represent the minimum and maximum levels seen in standard industry practice. The range of tests used to characterise the near surface performance include subjective assessment of surface quality, surface hardness and surface tensile strength. Permeability studies of the liners after casting indicate that no excessive embedding of fine particles occurred irrespective of constituents used. Surface quality was dramatically improved in each case and changes to surface colour through densification were quantified. Near surface performance studies indicated a significant improvement for all systems studied.

An Investigation into the critical factors affecting the performance of composite controlled permeable formwork liners: Part I – Drainage medium

The critical elements associated with a CPF drainage medium and their associated effects on the near surface performance of vertically cast concrete slabs are the focus of this study. A range of board absorption levels, textured features and texture depth are investigated using a Taguchi orthogonal array approach. A permeable polypropylene filter layer was used in conjunction with the various drainage mediums. Statistical software was utilised to determine significant variables as a function of the near surface performance. The range of tests used to characterise the surface performance of the various drainage mediums include surface roughness, surface hardness, surface tensile strength and water absorption. Results are compared to a control sample which was cast against impermeable plywood formwork. All drainage medium permutations showed similar evidence of water/cement ratio reduction at the near surface region of the concrete slab. Surface quality was analysed using quantitative methods and showed significant improvements for all systems over the control. The results for the systems studied indicate that the features of a drainage medium are not critical to the functionality of a CPF liner to reduce the near surface w/c ratio. In fact, it is indicated that the absence of a drainage medium has the same enhancement in near surface concrete slab properties as that of a complex structure when compared to the control sample.