This study reports an experimental investigation designed to assess the influence of near-surface moisture contents on permeation properties of alkali-activated slag concrete (AASC). Five different drying periods (5, 10, 15, 20 and 25 days) and three AASC and normal concretes with compressive strength grades ranging from C30 to C60 were considered. Assessment of moisture distribution was achieved using 100 mm diameter cores with drilled cavities. Results indicate that air permeability of AASC is very sensitive to the moisture content and its spatial distribution, especially at relative humidity above 65%. To control the influence of moisture on permeation testing, the recommendation of this paper is that AASC specimens should be dried in controlled conditions at 40 o C for 10 days prior to testing. It was also concluded from this study that AASC tends to perform less well, in terms of air permeability and sorptivity, than normal concrete for a given strength grade. This conclusion reinforces the need to further examine AASC properties prior to its widespread practical use.

There is an increasing interest in hierarchical design and additive manufacturing (AM) of cement-based materials. However, the brittle behavior of these materials and the presence of interfaces from the AM process currently present a major challenge. Contrary to the commonly adopted approach in AM of cement-based materials to eliminate the interfaces in 3D-printed hardened cement paste (hcp) elements, this work focuses on harnessing the heterogeneous interfaces by employing novel architectures (based on bioinspired Bouligand structures). These architectures are found to generate unique damage mechanisms, which allow inherently brittle hcp materials to attain flaw-tolerant properties and novel performance characteristics. It is hypothesized that combining heterogeneous interfaces with carefully designed architectures promotes such damage mechanisms as, among others, interfacial microcracking and crack twisting. This, in turn, leads to damage delocalization in brittle 3D-printed architectured hcp and therefore results in quasi-brittle behavior, enhanced fracture and damage tolerance, and unique load-displacement response, all without sacrificing strength. It is further found that in addition to delocalization of the cracks, the Bouligand architectures can also enhance work of failure and inelastic deflection of the architectured hcp elements by over 50% when compared to traditionally cast elements from the same materials.

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...

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