Valeria Corinaldesi

Recycling of rubble from building demolition for low-shrinkage concretes

In this project concrete mixtures were prepared that were characterized by low ductility due to desiccation by using debris from building demolition, which after a suitable treatment was used as aggregate for partial replacement of natural aggregates. The recycled aggregate used came from a recycling plant, in which rubble from building demolition was selected, crushed, cleaned, sieved, and graded. Such aggregates are known to be more porous as indicated by the Saturated Surface Dry (SSD) moisture content. The recycled concrete used as aggregates were added to the concrete mixture in order to study their influence on the fresh and hardened concrete properties. They were added either after water pre-soaking or in dry condition, in order to evaluate the influence of moisture in aggregates on the performance of concrete containing recycled aggregate. In particular, the effect of internal curing, due to the use of such aggregates, was studied. Concrete behavior due to desiccation under dehydration was studied by means of both drying shrinkage test and German angle test, through which shrinkage under the restrained condition of early age concrete can be evaluated.

Use of rubble from building demolition in mortars.

Because of increasing waste production and public concerns about the environment, it is desirable to recycle materials from building demolition. If suitably selected, ground, cleaned and sieved in appropriate industrial crushing plants, these materials can be profitably used in concrete. Nevertheless, the presence of masonry instead of concrete rubble is particularly detrimental to the mechanical performance and durability of recycled-aggregate concrete and the same negative effect is detectable when natural sand is replaced by fine recycled aggregate fraction. An alternative use of both masonry rubble and fine recycled material fraction could be in mortars. These could contain either recycled instead of natural sand or powder obtained by bricks crushing as partial cement substitution. In particular, attention is focused on the modification that takes place when either polypropylene or stainless steel fibers are added to these mortars. Polypropylene fibers are added in order to reduce shrinkage of mortars, stainless steel fibers for improving their flexural strength. The combined use of polypropylene fibers and fine recycled material from building demolition could allow the preparation of mortars showing good performance, in particular when coupled with bricks. Furthermore, the combined use of stainless steel fibers and mortars containing brick powder seems to be an effective way to guarantee a high flexural strength.

Environmentally-friendly mortars: a way to improve bond between mortar and brick

In order to find new application fields for either fine materials coming from building demolition or industrial byproducts, some mortars, in which fine recycled materials, obtained from a plant where rubble from building demolition are ground, are substituted to natural sand, were tested.Moreover, mortars containing either fly ash or ground brick powder as partial cement replacement were studied.Based on characterization results and performance evaluations, recycled-aggregate mortar seems to be superior in terms of mortar-brick bond strength, mainly because of its rheological properties.In addition, the use of fine recycled aggregate instead of natural sand is in accordance with the sustainable development concept, with recycling and reuse of building rubble playing a key role in meeting the need to complete the building life cycle.RésuméEn vue de trouver de nouveaux domaines d’application pour les déchets de démolition ou pour quelques sous-produits industriels, des mortiers ont été produits. C’est dans ceux-ci que, par rapport à un mortier traditionnel à base de ciment, on a étudié le remplacement du sable naturel par la fraction fine recyclée obtenue d’une installation de recyclage, dans laquelle les déchets de démolition sont concassés.En outre, on a étudié des mortiers contenant soit des cendres volantes, soit de la poudre de briques concassées au lieu du ciment. En les comparant selon les résultats de la caractérisation et selon l’évaluation des performances, les mortiers avec granulats recyclés semblent les meilleurs aux termes de la tension d’adhérence entre le mortier et la brique, due à ses propriétés rhéologiques.De plus, l’usage de la fraction fine des granulats recyclés au lieu du sable naturel correspond à la notion du développement soutenable et le recyclage et le réemploi des déchets de démolition jouent un rôle clé dans la fermeture du cycle de vie des bâtiments.

Structural Concrete Prepared with Coarse Recycled Concrete Aggregate: From Investigation to Design

An investigation of mechanical behaviour and elastic properties of recycled aggregate concrete (RAC) is presented. RACs were prepared by using a coarse aggregate fraction made of recycled concrete coming from a recycling plant in which rubble from concrete structure demolition is collected and suitably treated. Several concrete mixtures were prepared by using either the only virgin aggregates (as reference) or 30% coarse recycled aggregate replacing gravel and by using two different kinds of cement. Different water-to-cement ratios were adopted ranging from 0.40 to 0.60. Concrete workability was always in the range 190–200 mm. Concrete compressive strength, elastic modulus, and drying shrinkage were evaluated. Results obtained showed that structural concrete up to C32/40 strength class can be manufactured with RAC. Moreover, results obtained from experimentation were discussed in order to obtain useful information for RAC structure design, particularly in terms of elastic modulus and drying shrinkage prediction.

Paper Mill Sludge Ash as Supplementary Cementitious Material

Paper mill sludge is often incinerated for heat recovering and also for an important volume reduction. In Italy about 6x10 5 tons of paper sludge is yearly produced giving 60kg of paper ash per ton. In this project, the ash coming from burning of paper mill sludge from primary mechanical separation process, fired as single fuel, was studied in order to evaluate its use as supplementary cementitious material in concrete manufacturing. On the basis of the data collected it can be concluded that the paper mill sludge ash, if replaced by 5 to 10% of Portland cement, show a positive effect on the mechanical performance of the concrete. On the other hand, due to its high fineness and consequently high water absorption, it requires a higher dosage of water, so that the use of paper ash should not be higher than 10% by weight of cement.

Thaumasite: evidence for incorrect intervention in masonry restoration

Abstract Thaumasite, as well as ettringite, are compounds which are increasingly found as deterioration products of cementitious materials subjected to sulfate attack. Thaumasite, and especially ettringite, have been abundantly reported in relation to concrete deterioration as well as, more recently, to the deterioration of cementitious mortars for masonry and for plasters. In particular, the problem appears serious in the field of repair of historical buildings, where the cementitious mortar can easily deteriorate just because of the formation of ettringite and thaumasite. However, although thaumasite is responsible for deterioration, in most cases, it may not be detected since it can be partially or almost completely removed by atmospheric agents. Many causes can be responsible for the presence of sulfates in masonry. At the same time, mortar and plaster are, in most cases, sources of calcium carbonate. Moreover, masonry is typically a porous material, which can be easily permeated by water, either rising groundwater or falling rainwater. Therefore, when cement based materials, which are in turn sources of calcium aluminates and calcium silicates, are used as binders, all of the ingredients necessary to cause thaumasite formation are present. Consequently, a compatibility issue emerges, which if not kept into proper account, will lead sooner or later to ineffective intervention.

Influence of recycled coarse aggregates characteristics on mechanical properties of structural concrete

This work studies with the influence of recycled coarse aggregates features on the mechanical properties of structural concrete. Recycled concrete is characterised by replacing different percentages of natural coarse aggregate with recycled coarse aggregate (0, 20, 50 and 100%) and two different water-to-cement ratios .50 and .65. The experimental program was carried out at the two laboratories: one at the University of A Coruña and another at the Università Politecnica delle Marche (Italy). For said purpose, two different recycled aggregates were used, with different water absorptions and compositions. Results obtained allowed the authors to establish different mechanical behaviour of recycled concrete (compressive strength, tensile splitting strength and modulus of elasticity) due to different replacement percentages and characteristics of the recycled aggregates.

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.

Evaluation of Recycled Aggregate Concrete Cracking through Ring Test

Cracks can reduce the service life of a concrete structure by allowing aggressive agents to penetrate through it in easy ways. Free shrinkage evaluation alone is not enough to determine if cracking can be expected in a structure since concrete creep behaviour, stiffness and toughness also influence the potential for cracking. Consequently, it is rather interesting to perform restrained shrinkage tests, such as the ring test according to ASTM C 1581–04. The testing procedure involves concrete ring specimens restrained by an inner steel ring on which strain gauges are placed to determine the age of cracking, since abrupt changes in the steel strain occur when concrete is cracked. Both the ring test and free shrinkage test should be carried out in the same exposure conditions, 21°C and 50% relative humidity. Moreover, compressive and tensile strengths of concrete were evaluated on cubic specimens at the time of its cracking and up to 28 days of curing. By means of analytical and numerical models of the ring specimen, some useful information on the stress induced in the material and on the tensile creep behaviour of concrete can be extrapolated thus allowing to better interpret the experimental results. This experimental procedure enables to study the influence of concrete mixture composition on the potential for early-age cracking of concrete. In particular, in this work the influence on early-age cracking of recycled-concrete aggregate partially replacing virgin sand was tested.