Development of a new in situ test method to measure the air permeability of high performance concretes

Abstract

Although several in situ techniques, including the Autoclam Permeability System, are available to examine normal concretes (NCs) for this purpose, none are sufficiently sensitive to quantify and distinguish relative high performance concrete (HPC) performance. Therefore, to assess the HPC performance characteristics using the Autoclam air permeability test methodology, two key modifications were investigated and a new test protocol developed. The first modification considered a reduced volume of compressed air applied to the test area (named LV test), and the second an increased test area (named A-75). The reliability of the proposed modifications was investigated by comparing against a laboratory-based gas permeability test method (RILEM air permeability test).Surface resistivity and relative humidity were assessed to evaluate the influence of moisture conditions on in situ air permeability test results. A strong correlation between LV test and RILEM air permeability test results was found when the free moisture near concrete surface regions (up to 20 mm) was removed. It was concluded that the LV test exhibits strong potential to become an established method for assessing in situ HPC permeability. Key wordsIn situ air permeability test, high performance concrete, relative humidity, surface resistivity, RILEM gas permeability test, Autoclam air permeability test Page-2 IntroductionHigh performance concretes (HPCs) are typically designed with superior performance characteristics relative to normal concretes (NCs) [1][2][3]. Resulting enhanced durability of concrete structures containing HPCs is a key driving force behind their application [2,3]. This is particularly relevantgiven the large sums of money spent annually on repairing and maintaining structures worldwide [4,5]. Various grades of HPCs can be designed, manufactured and tested in laboratory conditions to satisfy design specifications for different service conditions [2,6,7]. However, it is not safe to assume at all times that pre-specified durability levels are achieved on site, as ultimate engineering concrete properties are not solely related to materials, mix proportions and service environments, but also factors which are difficult to control on site, such as manufacturing and delivery processes, as well as construction practices employed from initial placement to final curing [4,8,9]. As a result, a correlation between performance assumptions and in situ construction quality should ideally be considered.To ensure the ultimate delivery of high performance in practice, on site evaluation is essential and so were many field techniques proposed [10][11][12][13][14]. Amongst these, assessment of concrete's near-surface permeation characteristics is recognised as a reliable tool to qualify durability [4,10,14,15], because deterioration of reinforced concrete usually involves ingress of aggressive substances from the surrounding environment [3,5,7,11]. Air permeability tests have gained popularity in recent years due to their short test duration a...

Establishment of a preconditioning regime for air permeability and sorptivity of alkali-activated slag concrete

“…From previous research, a drying temperature of 40 o C has been reported as appropriate for minimising cementitious microstructural alteration and capable of determining free moisture contents of NC and AASC samples [11,27,30] and removing moisture effects on permeation results of a range of concrete types [11,29]. As such, the temperature of 40 o C was chosen as the pre-conditioning drying temperature for AASC in this study.…”

“…To assess gel porosity, the cores were then placed in an oven at 105 o C to reach the mass equilibrium state (M105C). These procedures were developed based on the previous studies [11,27,29,30]. …”

“…The mean value of three measurements was reported along with the average error. Figure 3 shows the surface mounted air permeability test instrument used in this study to assess both AASC and NC, further details of which are reported in the literature [29]. The test area considered was the inner 50 mm circle of the 100 mm cylindrical specimen, isolated using a base ring.…”

“…In general, capillary porosity refers to the pore space occupied by water held by capillary force, the removal of which does not need high energy [25]. Previous researches [11,29,30] show that this property was estimated by drying saturated samples and measuring the weight loss under 40-50 o C and this weight loss is taken as an estimate of porosity of the capillary system. According to this, the gel pores were determined by the moisture loss under 40 o C and 105 o C, as the capillary pores and gel pores are two main types in concrete.…”

“…As such, AASC physical and chemical properties might be significantly changed, meaning that pre-conditioning procedures may impact test results and give potentially misleading conclusions regarding long-term in-service performance [27,28]. Meanwhile, the correct interpretation of permeation test results requires determination of internal moisture content and its distribution [11,29]. This is a further area where in-depth research is lacking for AASC.…”