Combined experimental and numerical study on micro-cube indentation splitting test of cement paste

Abstract

The aim of this paper is to investigate the fracture performance of cement paste at micro scale by both experimental and numerical methods. Micro cubic specimens with length of 100 µm were fabricated by precision cutting, grinding and micro-dicing, and tested by splitting with a wedge tip mounted on a nano-indenter. A nominal splitting tensile strength was derived from the maximum load of the recorded load-displacement diagram to represent the global fracture performance of the fractured micro-cube. To achieve this, an analogy was made between the microcube indentation splitting test and the standard Brazilian splitting test. To cope with the inherent heterogeneity of this material at micro scale, for cement paste with each water/cement (w/c) ratio (0.3, 0.4 and 0.5), more than hundred micro-cube specimens were fabricated, tested and analysed using Weibull statistics. The analysis shows that the splitting tensile strength of cement paste on the micro scale is much higher than on the macroscopic scale but lower than tensile strength of distinct hydrated cement phases measured on micro or nano scale. Furthermore, higher and less scattered values of splitting tensile strength were observed for the specimens with lower w/c ratio. In parallel with the experiments, a micro-structure informed lattice fracture model was adopted to simulate the fracture process of the micro-cube under indentation splitting. The simulated results were compared with the experimental one and have a good consistency in terms of the load-displacement curve and fracture pattern. With the method presented in this paper the framework for validation of the modelling results at micro scale is created.

Experimentally informed fracture modelling of interfacial transition zone at micro-scale

“…The hydration degree is quite close to the results (63.0%) reported by Haecker et al [39] using non-evaporable water content method. Due to the limitation of image resolution, pores smaller than 2 mm are not detectable and are mixed within the segmented solid phases [40][41][42]. Therefore, the total porosity derived from CT images is significantly lower than the theoretical total porosity predicted by Powers model (17.80%) [43] and mercury intrusion porosimetry (MIP) (17%) [44].…”

“…Recent reports document the utilization of nanoindenter as a versatile instrument for loading micrometre sized specimens [37][38][39][40][41][42][43]. The specimens can be prepared either by a focused ion beam (FIB) milling technique [37][38][39] or physical micro-dicing procedure [40][41][42][43]. The FIB milling technique uses a focused Ga-ion beam for precise micromachining of various materials to fabricate specimens with designed geometries, typically the micro-cantilever [37,38] and micro-pillar [39].…”

Towards understanding stochastic fracture performance of cement paste at micro length scale based on numerical simulation

“…Although 10 specimens covering 10 5 mm 3 were extracted from the segmented images for each w/c ratio, still a bit difference of the averaged volume fraction of porosity and anhydrous cement particle were found between the investigated 10 specimens and the scanned prism (Table 1). Recently, such high tensile strengths were experimentally observed by rupturing the same size specimens through a nanoindentation system [18]. Furthermore, even higher strength is expected for samples at smaller length scale (few microns) [57], where distinct cement hydration phases like inner and outer hydration products containing capillary and gel pores can be sampled as micro cantilever beams.…”

“…Furthermore, for a number of reasons that include problems with producing and measuring miniaturized mechanical samples, the predicted mechanical properties are difficult to verify experimentally at the micro scale. As reported in [17,18], a pioneering work on experimental micromechanics of cement paste has been conducted at the Delft University of Technology. Micrometre scale specimens with a cubic dimension of 100 mm were produced by a micro dicing saw and ruptured by a diamond wedge tip mounted on a nanoindentation system.…”

Use of X-ray computed tomography as input for fracture modelling of cement paste-aggregate interface

“…In total, 9 types of elements as listed in Table 1 were considered. For the elements that exist in the cement matrix, their mechanical properties have been calibrated and validated in the authors' previous works [3][4][5]. With respect to the element within the aggregate, its elastic modulus is taken from [6].…”