ACTUAL SITUATION OF THE STATE OF THE ART PREPARED BY THE TC-217, PROGRESS OF RECYCLING IN THE BUILT

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1 ACTUAL SITUATION OF THE STATE OF THE ART PREPARED BY THE TC-217, PROGRESS OF RECYCLING IN THE BUILT ENVIRONMENT Enric VAZQUEZ (1) (1) Department of Construction Engineering, Materials Section, Universitat Politecnica de Catalunya, Barcelona, Spain Abstract The RILEM TC-217 is preparing a State of the Art about Recycling in the Built Environment. This task will be finished in December 2010 and will include a selection of the publications and projects made in this field in the last years. For the keynote lecture in Shanghai the author has selected some very recent works that represent an example of the end RILEM publication. The end publication will include topics of the Shanghai Congress. Now we include the problem with gypsum, a new automated test method for saturated surface dry density for recycled aggregate, construction products from waste fines, geologic characterization of concretes with recycled aggregates, and some observations about the durability of concretes with recycled aggregates. 1. SELECTION FOR PRESENTATION After studying the contributions made during the activity period of the TC 217, we hereby present a short selection of the ones that shall be included and developed during the State of Art that will end in December The problem with gypsum - A new automated test method for saturated surface dry density for recycled aggregates. - Construction products from waste fines. - Reologic Characterization of Concretes with recycled aggregates. - Some observations about the durability of concretes with recycled aggregates 1

2 2. THE PROBLEM WITH GYPSUM Gypsum is being used increasingly as a building material because of its favorable properties. If these building materials are not selected during demolition or not removed during processing then the recycled building materials produced cannot be used because, for one thing, they do not fulfill environmental requirements. Apart from this there are also problems that lead to the formation of secondary ettringite, which initiates expansion phenomena both in concretes and in unbound base courses.this is a capital problem in Spain and Eastern Germany. In Spain the GEAR PROJECT has detected a medium content of gypsum in the products of the 65 recycling plants analyzed of 1,2 weight% in pure concrete, but 2,9 in aggregates containing concrete and a maximum content of 30% of ceramic elements. In this last category of mixed recycled aggregates the minimum and maximum values go from 1 to 7,2 %. The values determined in Eastern Germany are 2,73% as medium content in concrete aggregate and minimum and maximum values from 1,8 and 5,35 weight %. Müller, A./ Schnellert,Th. / Kehr,K. have published on their research Gypsum constituents in recycled concrete origin, effects and removal by jigging. The separation process makes use of the different densities of the solid components that are present alongside one another in a mixture of materials. During the jigging process the mixture of particles to be sorted is loosened by a pulsating stream of water. The lighter particles are discharged over a weir. The heavier particles are drawn off in the lower part of the jig bed. The material in the jigging machine is supported on a sieve tray. Figure 1: Jigging The jigging process is affected by the properties of the feed material, as density/particle size/particle shape and process parameters as stroke frequency. The differences in density 2

3 which are necessary for jig sorting in water can be estimated with the aid of the following quotient: ρl: density of the lighter component ρh: density of the heavier component ρw: density of water q= ρl-ρw/ρh-ρw (1) The following ranges apply: q > 2,5 separation down to particle sizes of about 100ųm q > 1,5 separation down to particle sizes of about 1.5 mm q < 1,5 no separation possible by jigging The bulk densities of the materials under investigation varied between the highest value of 2.40 g/cm3 measured for the railway sleeper concrete to the lowest value of 1.56 g/cm3 measured for the gypsum building material from the bath. The values obtained after one and two passes were: Table 1: Values obtained after one and two passes Mass % gypsum Mean value Min. value Max. value in starting material 2,7 1,8 5,4 after one pass 0,78 0,78 0,75 after two passes 0,61 0,62 0,59 It is clear that the reduction in the gypsum content is possible. This can be achieved either by intermediate stockpiling of the material and feeding it through the machine again or by two jigging machines connected in series. Trials were also carried out to find the influence of the par- ticle size using the 3-component feed material consisting of concrete, brick and gypsum building material. In this case the machine settings had to be changed for sorting the 2/4 mm fraction. As far as the machine settings were concerned it was found that the mechanically adjustable parameters, such as the dimensions of the feed and outlet openings and the position of the float weight, had little effect on the jigging result. The influence of the stroke frequency and the layer thickness of the jig bed, which could be adjusted at the control system, was more significant. Good separation results were achieved with average stroke frequencies of 70 to 80 strokes per minute and layer thicknesses that remained less than 95 mm. Superimposition of classification on top of the jigging process led to significant differentiation between the particle size distributions of the product and the feed material. 3

4 For application of the process it therefore follows that it is essential first to produce a feed material in the size range 4/32mm or 4/45 mm. In the experimental investigations carried out with the Triple A jigging machine it was shown that the gypsum content in the product can be reduced significantly when compared with the feed material. Concrete from the demolition of prefabricated buildings, which depending on its origin may contain high levels of gypsum, can be freed from gypsum particles in this way and made useable. 3. AN AUTOMATED METHOD FOR RECYCLED AGGREGATE DENSITY SSD EN 1097 provides test methods for aggregate density, intensive and time consuming for the fine fraction with d<4mm. An automated method is introduced by Hlawatsch,F./ Aycil,H./ Kropp,J., which is based on the drying behavior of granular porous materials. For recycled aggregates a good correlation is found between the EN 1097 method and the proposed method. The principle of evaluation is well reflected in the following figures. Figure 2: Principle of the test 4

5 Figure 3: Drying rate during the test Figure 4: Automated determination of ssd: Test se up The ss condition can be easy determined and time saving. 4. THE USE OF FINE FRACTION OF RECYCLED AGGREGATES In the following we would like to point out some interesting features of the fine fraction of C&D waste and other fine mineral wastes from other industrial sectors to be used in the production of construction products. The presentation of J.Kropp in Sao Paulo

6 summarizes a number of research projects on this topic carried out in Bremen, mostly a cooperation between the Bremen State Office for Materials testing and Hochchule Bremen. The major constituents and phases in recycled aggregate fines from concrete are calcium silicate hydrates, calcium aluminate hydrates, gypsum, calcium hydroxide and natural sand. In that case of calcium silicate bricks are calcium silicate hydrates and silicates. In AAC blocks calcium silicate hydrates, aluminates and sulfates. In plaster and mortars, we can find calcium silicate hydrates, gypsum and natural sand. All the prevailing phases have hardening potentials. The hardening and strength gain of these fines can be reached under hydrothermal conditions in an autoclave. We can achieve the formation of new phases in pozzolanic reactions and the re-arrangement and recrystallisation of prevailing phases. The technology is the same as in the case of calcium silicate bricks. In the next figure we can see the effect of the different type of fines at 200ºC in 12 hours. Figure 5: Effect of type of fines in compressive strength Profound changes in the micro-structure of the fines will occur during the treatment. In the following figure we can see the effect of different times on pore size distribution. The process can be optimized by adjusting the parameters consolidating pressure, water content, CaO/SiO2 ratio, maximum curing temperature, duration of the treatment and grain size distribution. In general the finer the better. 6

7 pore size distribution relative pore volume [mm³/g] pore radius [nm] B1 SL A4 M2-0h M2-2h M2-4h M2-6h M2-12h M2-24h Figure 6: Changes in pore size distribution 5. REOLOGICAL CHARACTERISATION OF CONCRETES WITH RECYCLED AGGREGATES This presentation corresponds with the first results of the collaboration project between the USP (Sao Paulo) and the UPC (Barcelona). The authors are from USP: Vanderley M. John, Antonio d. de Figueiredo, Rafael G. Pileggi, Lucia H. Higa, and from UPC: Enric Vazquez, Marilda Barra. Five concretes with conventional and recycled aggregates were tested in the reometer developed in the USP. The concretes correspond in composition to following qualities and values. Table 2: Aggregate 4mm Processing Slump mm Nat Natural Natural 95 SPB Recycled SaoPaulo Crushing 87 MB Recycled Macae Crushing 82 7

8 Table 3: Type of Aggreg Cement Sand Aggregate w/c -ate Nat 1 2,25 3,25 0,73 SPB 1 2,25 2,50 1,00 MB 1 2,25 2,36 1,08 SPJ 1 2,25 2,78 0,87 MJ 1 2,25 2,67 0,87 A slump= 80±10 mm was reached in all the concretes adding water. The proportions are expressed in volum.after 28 days the concretes reached the following compressive strength. Table 4: Concrete Nat SPJ SPB MJ MB MPa 21,5 18,1 15,6 16,6 14,9 The developed reometer is based in shear cycles acceleration/deceleration. 50,100,150,250,500,1000,750,500,250,150,100,50 rpm were applied, with 20 s every rotation and 10min between 1st and 2nd cycle. Figure 7: Reometer USP After the 1st and 2nd cycle the following results were registered. 8

9 Figure 8: First Cycle Figure 9: Second Cycle At higher rotation levels differences between the reference concrete and those made with recycled aggregates at higher rotation levels were observed. Nat has a pseudo plastic behaviour and the recycled concretes behave as Bingham fluids. Excess of water in the Recycled Concretes originated by the needs of slump test (aggregate form) are responsible. 2nd cycle shear strength level is reduced because we have a disaggregation. 9

10 The use of slump test penalizes the compressive strength of the recycled concretes by addition of an excess of water. We can obtain good workability and higher compressive strength if we use the Reometer criteria. We are developing a complete and simple methodology. 6. OBSERVATIONS ABOUT DURABILITY 1. Our quality concept is based on comparing with natural aggregates and not always related with the real performance needs of the product use. A good example is in the freeze and thaw standard: Pre drying at 105ºC of recycled concrete aggregate is too severe and unnecessary for the real exposure consideration. We will have erroneous conclusions about the behaviour in real conditions. 2. Example of Bound Applications: After the preliminary durability tests you may perhaps use the performance concept instead of the prescription concept. You may obtain unexpected good results, that in some cases can be related with the chemical activity of the fines of RCA or ceramic grains 3. Chloride penetration: Very recent studies obtained that for the w/c ratios between 0,45 and 0,55, normal in Civil Engineering works, the chloride penetration depends more from the w/c than from the quantity of recycled aggregate present Very often the results depend from the differences between test methods. Recycled aggregates are penalized and not every time this corresponds to the real behaviour. 10