Piet Stroeven

Development of hybrid polypropylene-steel fibre-reinforced concrete

Abstract This research first investigates the optimization of fibre size, fibre content, and fly ash content in hybrid polypropylene-steel fibre concrete with low fibre content based on general mechanical properties. The research results show that a certain content of fine particles such as fly ash is necessary to evenly disperse fibres. The different sizes of steel fibres contributed to different mechanical properties, at least to a different degree. Additions of a small fibre type had a significant influence on the compressive strength, but the splitting tensile strength was only slightly affected. A large fibre type gave rise to opposite mechanical effects, which were further fortified by optimization of the aspect ratio. There is a synergy effect in the hybrid fibres system. The fracture properties and the dynamic properties will be further investigated for the hybrid fibres concrete with good general mechanical properties.

Assessment of packing characteristics by computer simulation

Abstract Most relevant engineering mechanical properties of normal concretes such as compressive strength are to a large extent governed by the density and the uniformity of the aggregate packing as the load-bearing structure. Nevertheless, the integrity of this skeleton will gradually break down under increased loadings. In cementitious materials this is due to debonding of particle-matrix interfaces, which leads to crack initiation and propagation in the so-called interfacial transition zone. The strength of the interfacial transition zone on a structural level is also governed by the density and the uniformity of the packing of (blended) cement particles in the neighbourhood of aggregate surfaces. However, particularly structure-sensitive properties like cracking and tensile strength are also, and to a disproportional degree, influenced by the nonuniformity of the particle packing. This is true for microcracking that results from packing discontinuities in the binder near particle interfaces, as well as for engineering cracking at the concrete elements surfaces due to aggregate-packing discontinuities near the mould. The SPACE system (Software Package for the Assessment of Compositional Evolution) has been developed to assess the characteristics of dense random-packing situations in opaque materials by a “realistic” structural simulation. This paper presents a short introduction to the system and deals only with the essential design features. Next, an application addressing the particle-packing problems demonstrates the systems capabilities.

Fracture properties of concrete reinforced with steel–polypropylene hybrid fibres

Abstract This research discusses polypropylene fibres and three sizes of steel fibres reinforced concrete. The total fibre content ranges from 0% to 0.95% by volume of concrete. A four-point bending test is adopted on the notched prisms with the size of 100×100×500 mm 3 to investigate the effect of hybrid fibres on crack arresting. The research results show that there is a positive synergy effect between large steel fibres and polypropylene fibres on the load-bearing capacity and fracture toughness in the small displacement range. But this synergy effect disappears in the large displacement range. The large and strong steel fibre is better than soft polypropylene fibre and small steel fibre in the aspect of energy absorption capacity in the large displacement range. The static service limitation for the hybrid fibres concrete, with “a wide peak” or “multi-peaks” load–CMOD patterns, should be carefully selected. The ultimate load bearing capacity and the crack width or CMOD at this load level should be jointly considered in this case. The K IC and fracture toughness of proper hybrid fibre system can be higher than that of mono-fibre system.

Strength and durability aspects of calcined kaolin-blended Portland cement mortar and concrete

Abstract Economic and sustainability arguments require carefully assessing the potentialities of indigenous resources for the production of mortar and concrete for the construction industry. In Vietnam, significant efforts should be bestowed on urban development, coastal protection and harbour construction works. In a joint Vietnamese-Dutch co-operation program, the practical use for this purpose of relevant resources in Northern Vietnam is assessed experimentally. This paper concentrates on kaolin, which is widely available in this region. The key issues this paper is dealing with are the effects of partial replacement of Portland cement by calcined kaolin in mortar and concrete on compressive strength as well as on durability characteristics of mortar and concrete mixes pertinent to the coastal environment. Workability measures are also mentioned. Data are therefore presented on compressive strength development over a maximum curing period of 180 days of mixes in which the water to binder ratio was varied between 0.40 and 0.53. Moreover, partial replacement was considered in the range from 0% to 30% by weight. The results of this study render possible the assessment of optimum replacement percentages of Portland cement by calcined kaolin, and the associated strength gain. Additionally, this paper reports on the performance aspects of similarly blended mortar and concrete specimens stored for a period of one year in a low concentration of a sodium sulfate solution. It could be concluded that a strength gain due to blending will be accompanied by improved durability in this environment.

Reconstructions by SPACE of the Interfacial Transition Zone

Abstract Of particular interest in concrete technology is the so-called Interfacial Transition Zone (ITZ). Conflicting experimental evidences as to the internal structure and extent of the ITZ, and even as to the very existence of it, make it attractive to confront such observations with a coherent picture of the ITZ produced by computer-simulation, although based on a simplified model concept. This contribution outlines the scientific framework for interpretation of the so-called packing phenomenon. A dynamic computer-simulation system, Software Package for the Assessment of Compositional Evolution, with the acronym SPACE was recently developed by the second author, and has been used for the present purpose. In addition to properly simulating composition of particulate materials, as can also be achieved by conventional systems based on random sequential procedures, it has been demonstrated earlier that SPACE can also more accurately reproduce configuration of particles in such materials. An hydration algorithm is additionally implemented in SPACE. Some preliminary information on gradient structures in the ITZ are discussed. The extent of packing gradients in the fresh and hardened state will be shown to vary with changes in material composition (water to cement ratio, cement fineness) and in the configuration-sensitivity of the parameter being studied. This implies structural gradients to extend further away from aggregate grain surfaces the more sensitive the very parameter is to packing configuration. Particular emphasis is given to this fundamental aspect, and not to properly estimating the ITZs thickness of this model cement paste near boundaries. Tools are provided to extract 2-D structural data from imaginary section planes (or from imaginary thin section projections) of the ITZ parallel to the interface. By making use of stereological methods, such data are given a 3-D structural meaning. Of course, direct information on porosity, packing characteristics and local particle distributions is available in 3-D. Therefore, in some cases direct 3-D measurements are possible, as well as visualisation of parts of the structure.

The Mount Feather Diamicton of the Sirius Group: an accumulation of indicators of Neogene Antarctic glacial and climatic history

Abstract A paucity of data from the Antarctic continent has resulted in conflicting interpretations of Neogene Antarctic glacial history. Much of the debate centres on interpretations of the glacigene Sirius Group strata that crop out as discrete deposits along the length of the Transantarctic Mountains and in particular on its age and the origin of the siliceous microfossils it encloses. Pliocene marine diatoms enclosed within Sirius Group strata are inferred to indicate a dynamic East Antarctic ice sheet that was much reduced, compared with today, in the early–middle Pliocene and then expanded again in the late Pliocene. However, the geomorphology of the Dry Valleys region is interpreted to represent a relatively long-lived (middle Miocene–recent) and stable polar climatic regime similar to that of today. The Mount Feather Diamicton infills a palaeovalley at ca. 2500 m on the NE flank of Mount Feather in the Dry Valleys region and has been included within the Sirius Group. We obtained four shallow cores (COMRAC 8, 9, 10 and 11) from beneath the permafrost boundary in the Mount Feather Diamicton in order to understand its origin and relationship with the surrounding landscape. Detailed studies of these cores (stratigraphy, sedimentology, palaeontology, micromorphology, petrography and fabric) have yielded new data that demonstrate a much more complex climatic and glacial history for the Mount Feather Diamicton than in previous interpretations. The data indicate that the Mount Feather Diamicton was deposited beneath a wet based glacier fed from a larger ice sheet behind the Transantarctic Mountains. It is, however, unlikely that this ice sheet overtopped Mount Feather (2985 m). A near-in situ non-marine diatom assemblage was recovered from 90 cm depth in COMRAC 10 and indicates a maximum depositional age of Late Miocene for the Mount Feather Diamicton. A subsequent glacial episode has distributed a boulder blanket across the surface of the diamicton. Other post-depositional processes include drying, infilling of surface layers with aeolian sediment, and the development of melt-water runnels. We interpret these combined data to indicate the persistence of more temperate climatic and glacial conditions in the vicinity of Mount Feather until at least the Late Miocene.

Ash of vegetable waste used for economic production of low to high strength hydraulic binders

Abstract Some vegetable wastes contain relatively large amounts of silica. One of the most promising examples is rice husk. Since rice is a major crop among many of the developing countries, it is available in large quantities. Its ash can be produced without using expensive fuels—such as in the case of Portland cement. During incineration, heat is released which could eventually be transformed into mechanical energy for grinding the ash. An artificial pozzolan is obtained, which can be combined with lime to yield a hydraulic binder of lower quality. Kaolin clay, when available, could be added during incineration to improve the binder quality. At the other end of the spectrum, Portland cement can be blended with finely-ground rice husk ash to produce high strength concretes with a water reducing agent at low water to cement ratios. Blending with the incinerated kaolin can further increase cost effectiveness. This study concentrates on RHA technology but also gives a survey of obtained strength data.

Influence of Boundary Conditions on Pore Percolation in Model Cement Paste

Fresh model cement mixtures, with the same w/c ratio and particle size distribution, were simulated by the SPACE system that is based on a dynamic mixing algorithm. Thereupon, they were hydrated by the HYMOSTRUC 3D system. Boundary conditions were varied, rendering possible assessment of their influence on percolation of capillary porosity by serial sectioning and using the overlap of slices. Simulation results revealed increases in total porosity and in connected fraction of capillary pores due to the existence of aggregate. The de-percolation threshold of capillary porosity was found not only related to total porosity and image resolution, but also governed by the spatial distribution of capillary pores.

Geometric probability approach to the examination of microcracking in plain concrete

The paper aims at connecting in a quantitative way the engineering behaviour of plain concrete subjected to uniaxial compression to the main features of microcracking. The selected structural level conceives the concrete as a two-phase material, the smallest structural dimensions of which could be measured in millimetres. It is shown that geometric probability theory provides the basis for an elegant and general framework for the quantification of microcracking, and yet the image analysis procedures described rely exclusively on simple counting operations. Crack length (in a plane) and particularly specific crack surface area in connection with the specific surface area of the grains reveals information with respect to the intensity of structural loosening in the various load stages. The minor influence of the loading level is demonstrated to be reflected also by the small degree of orientation of the cracks. A simple concept for spacing is developed. Application shows the growing order in the crack structure under increasing load. Finally, the average crack length is determined. Since the probability density of crack length in a plane was shown to be governed by a simple exponential function, the maximum crack length could be determined in an equally simple way.

SPACE system for simulation of aggregated matter application to cement hydration

This paper presents the basic features of the Software Package for the Assessment of Compositional Evolution (SPACE). SPACE consists of a two-stage simulation strategy, providing successively for the three-dimensional packing of a particulate system and the structural evolution, the latter representing a sintering, foaming, or hydrating particulate system. Hence, SPACE has versatile potentialities. The initial distribution results from a generation process in which a predefined number of particles are dynamically mixed using a Newtonian motion model. Bulk material and interfaces can be simulated. The results obtained have been demonstrated to be realistic. Next, this paper deals with the simulation of cement hydration as an illustrative application of the SPACE system. The model starts with a simulated spatial distribution of anhydrous cement particles in a water-filled volume and simulates the hydration process through a series of relatively simple growth rules, which are iterated many times. The kinetic hydration model used here is similar to one used by van Breugel. The chemical reaction between cement and water results in expansion of the particle and in the formation of multiple contacts with other hydrating particles. The effects of this interparticle contact as well as the effect of water consumption on the hydration and expansion rate have been explicitly accounted for, with the aid of a surface sampling method that can efficiently evaluate the degree of contact between particles. Results from various numerical experiments will show the microstructural development in bulk and in the interfacial zone.