International Concrete Abstracts Portal

The paper deals with the study of rheological and mechanical properties of concretes manufactured by using wash waters as partial replacement of drinking water. Concretes were manufactured by using only water utilized to wash concrete mixing transport trucks. Three different wash waters, with solid residue amount in the range 0.13% - 5.5% by mass were used. The waters were directly sampled in an innovative beton wash system. 30 and 35 concrete grades were manufactured. The superplasticizer dosage was adjusted in order to attain a slump value of 210 mm (8.3 in.) at the end of the mixing procedure. The workability and workability loss up to 60 minutes were also evaluated. The compressive strength at 1, 7 and 28 days was measured on cubic specimens. At 60 minutes, fresh water was added to compensate slump loss (retempering procedure) and a second series of cubic specimens was taken to evaluate compressive strength penalization. Suspended solids in wash water strongly influences the workability retention: the higher the solid content, the lower the workability loss over time and, hence, the water demand to compensate the slump decrease. At the same w/c ratio, the presence of solid particles in wash water causes an increase in the early compressive strength. A modification of the aggregate grading curve, consisting in reducing the sand fine fractions, should be considered, to manufacture concretes comparable to traditional ones.

In this work, fiber reinforced SCLWAC (self-compacting lightweight aggregate concrete) mixtures were studied, in which synthetic fibers were used. Eight different SCLWAC mixtures were prepared, by employing either fly ash or silica fume as mineral addition. In particular, as aggregates, different combinations of fine and coarse expanded clay were tried, also partially replaced by either quartz sand or recycled aggregate coming from a recycling plant, in which rubble from concrete demolition are suitably treated. The SCLWACs were characterized at the fresh state by means of slump flow, V-funnel and L-box tests, and after hardening by means of compression, splitting tension and bending tests, as well as drying shrinkage measurements. Strength class of LC 45/50 was obtained by using synthetic macrofibres when the oven dry density of SCLWAC was about 1600 kg/m³ [2700 lb/yd³], while if the oven dry density of SCLWAC was lower than 1250 kg/m3 [2100 lb/yd³] a strength class of LC 25/28 was reached as well. Splitting tensile and flexural strength measured values were consistent with concrete strength class, while the elastic modulus was quite low with respect to normal weight self-compacting concrete (SCC). The post-cracking behaviour of SCLWAC resulted strongly improved by the addition of synthetic macrofibers, which proved to guarantee a softening behaviour in flexure. In conclusion, the addition of synthetic fibers allowed to design special concretes with excellent combination of mechanical and functional properties.

As residential and commercial buildings are responsible of a large energy consumption, especially for heating, Standards introduce limits to guarantee energy saving in new buildings; however, existing buildings need to be retrofitted for energy saving, given the large impact they have on the phenomenon. Under this perspective, in the framework of a European project, a multilayer prefabricated façade panel is proposed. It is characterized by an internal EPS layer, 100 mm [3.94 in.] thick, and by two external layers made of textile reinforced concrete (TRC), 12 mm [0.47 in.] thick. The insulating material is used to transfer the shear between the external TRC layers. The maximum size of the panel is 1.50 x 3.30 m² [60 x 130 in.²]; the panel height is properly chosen in order to fasten it to the frame concrete beams through four connectors placed near to the corners. In this paper the design of the panel and the results of tests performed on full scale panels are shown. The panels were fastened to the corners through suitable anchors and were loaded by means of a distributed load (considering wind pressure and suction as the main load acting on the panel).

In recent years the increasing interest for eco-sustainable building materials and the rising issue of plastic waste disposal are leading to the engineering of new composite construction materials incorporating post-consumer recycled plastics, able at the same time to meet new standard requirements, in terms of energy efficiency, and to reduce the consumption of natural resources. In the context of these issues, we have performed investigations on the effects of the addition of foamed artificial aggregates deriving from recycled plastic materials to a cementitious mortar. For this purpose, several mortar samples containing natural sand and different amounts (10, 25 and 50 % by volume) of foamed recycled plastic wastes were produced. The foaming of the recycled plastic waste was performed in laboratory by a foam extrusion process using a blowing agent (2 wt.%). An artificial aggregates particle size distribution similar to standard sand was used. Rheological and physical properties of lightweight mortar were studied. The improved surface roughness of foamed plastic aggregates ensures a more continuous interface and the presence of surface pores provides interlocking effect with cement paste. Replacement of natural sand by artificial aggregates produces a lightweight mortar but reduces mechanical properties.

One of the most important challenges for the cement industry is to find sustainable solutions to mitigate environmental footprint of its activities. Geopolymers are particularly attractive for this purpose; the use of waste as precursors, along with a room temperature curing, makes these materials low-polluting binders potentially suitable for sustainable building products. The lack of information on effective admixtures is limiting the practical acceptance of geopolymer concrete. The purpose of this paper is to study the influence of different superplasticizers, commonly used in Portland cement concrete technology, on properties of fly-ash based geopolymers. First, second and third generation superplasticizers (i.e., lignin-, naphthalene-, melamine-, polycarboxylic ether, acrylic based superplasticizers) have been used for the preparation of pastes and mortars. Two different amounts of admixture were tested: 0.6wt% and 1.0wt% by mass of binder. Among the investigated admixtures, the polycarboxylic ether based superplasticizer is the most effective. With a dosage of 1.0wt % by mass of fly ash it can be achieved an increase in workability of both geopolymer pastes and mortars without compromising the final strength of hardened material.