Jacopo Donnini

Reuse of recycled glass in mortar manufacturing

This work is aimed at studying the possibility of reusing waste glass from crushed containers as aggregate for preparing mortars. At present, this kind of reuse is still not common due to the risk of alkali–silica reaction (ASR) between alkalis of the cement and silica of the waste glass. This expansive reaction can cause great problems of cracking and, consequently, it can be extremely deleterious for the mortar durability. The influence of both size and colour of recycled glass coming from crushed containers on the durability of mortars is studied. The attention is focused on both mechanical behaviour, investigated by means of bending and compression tests, as well as durability, studied by means of accelerated tests for evaluating the tendency to expand under alkaline environment due to ASR. Several mortars are prepared by replacing at different rate the quartz sand with coarse glass cullet of different colours: clear (i.e. uncoloured), green and amber. Then, pulverised clear glass is added to the mortar mixtures, also in the presence of class F fly ash. Results obtained show that by using both green and amber glass cullet the mortars are stable, as well as by using powder glass, which also shows a significant pozzolanic effect. On the other hand, considerable expansion due to ASR is detected by using clear glass cullet.

Experimental study of adhesion between FRCM and masonry support

The use of composites with cement matrix seems to acquire an increasing interest in applications to masonry structures, due to their low impact, and a deeper understanding of the mechanical interaction between support and reinforcement is certainly necessary. The effectiveness of these interventions strongly depends on the bond between strengthening material and masonry, on the fibers/matrix interface, as well as on the mechanical properties of the masonry substrate [1]. In this work the attention was focused on the possible improvement of the bond between FRCM and masonry by means of an inorganic primer, which can be spread on the ceramic support before the application of FRCM reinforcement. Two different kinds of brick were tested, in order to simulate more or less porous masonry supports. Results obtained showed that, independently on the kind of brick used (more or less porous) the presence of an inorganic primer always improves bond between masonry support and the cementitiuos matrix of FRCM. In fact, the cementitous matrix of FRCM has been studied and optimized in order to guarantee the best fibers/matrix interface, while it is not necessarily the best option for improving the adhesion with the masonry support. In particular, very effective seems to be the use of very fine inorganic particles (at nanometric scale), which proved to be able to assure the best results in terms of bond strength. Also the fresh consistence of the primer seemed to influence the final result.

Binders alternative to Portland cement and waste management for sustainable construction—part 1:

This review presents “a state of the art” report on sustainability in construction materials. The authors propose different solutions to make the concrete industry more environmentally friendly in order to reduce greenhouse gases emissions and consumption of non-renewable resources. Part 1—the present paper—focuses on the use of binders alternative to Portland cement, including sulfoaluminate cements, alkali-activated materials, and geopolymers. Part 2 will be dedicated to traditional Portland-free binders and waste management and recycling in mortar and concrete production.

Study of physical and elasto-mechanical behaviour of fiber-reinforced concrete made of cement containing biomass ash

In this work, the influence of different kinds of fibres on Fibre-reinforced concrete (FRC) cracking behaviour is examined. Several FRC mixtures are designed, in which cement is partially replaced at 20% by weight of cement by a biomass ash coming from paper mill sludge incineration. These FRCs are prepared by alternatively using steel fibres, polypropilene macro-fibres, glass macro-fibres, as well as hybrid or bicomponent synthetic fibres. The dosage of fibres is always equal to .55% by concrete mixing volume. As reference, also a mixture with the same mixture proportions but without fibre reinforcement is prepared and tested. Ring test according to ASTM C 1581-04 and free shrinkage test are carried out in the same exposure conditions: 21 °C and 50% relative humidity. Moreover, compressive and tensile strengths of FRCs, as well as their elastic modulus, are evaluated on cubic specimens up to 28 days of curing, and, in particular, also at the time of ring cracking. In this way, other important information could be extrapolated by introducing these experimental data in suitable numerical model of the ring concrete specimens available in the literature. This procedure enables to study the influence of the kind of fibres on the potential for early-age cracking of concrete, as well as to identify the effect of tensile creep on concrete cracking. Results obtained show the effectiveness of the randomly dispersed fibres in counteracting the early cracking of FRC.

Bond Behavior of FRCM Carbon Yarns Embedded in a Cementitious Matrix: Experimental and Numerical Results

The use of inorganic cement based composite systems, known as Fiber Reinforced Cementitious Matrix (FRCM), is a very promising technique for retrofitting and strengthening the existing masonry or concrete structures. The effectiveness of FRCM systems is strongly related to the interface bond between inorganic matrix and fabric reinforcement, and, since the major weakness is often located on this interface, the study of stress-transfer mechanisms between fibers and matrix becomes of fundamental importance.FRCM are usually reinforced with uni-directional or bi-directional fabrics consisting of multifilament yarns made of carbon, glass, basalt or PBO fibers, disposed along two orthogonal directions. The difficulty of the mortar to penetrate within the filaments that constitute the fabric yarns and the consequent non-homogeneous stress distribution through the yarn cross section makes difficult to access the characterization of the composite material. The use of polymer coatings on the fibers surface showed to enhance the bond strength of the interface between fibers and mortar and, as a consequence, to improve the mechanical performance of the composite. The coating does not allow the mortar to penetrate within the filaments while is able to improve the bond between the two materials and to increase the shear stress transfer capacity at the interface.An experimental session of several pull out tests on carbon yarns embedded in a cementitious matrix was carried out. Different embedded lengths have been analyzed, equal to 20, 30 and 50 mm. The carbon yarns object of this study were pre-impregnated with a flexible epoxy resin enhanced with a thin layer of quartz sand applied on the surface.A variational model was proposed to evaluate the pull-out behaviour and failure mechanisms of the system and to compare numerical results to the experimental outcomes. Evolution of fracture in the yarn-matrix system is determined by solving an incremental energy minimization problem, acting on an energy functional which account for brittle failure of matrix and yarn, and for debonding at the yarn-matrix interface. The model was able to accurately describe the three phases of the pull-out mechanism, depending on the embedded length.