for Journal of Building Engineering Manuscript Draft

Elsevier Editorial System(tm) for Journal of Building Engineering Manuscript Draft Manuscript Number: JOBE-D-14-00052R2 Title: USE OF SYNTHETIC FIBERS IN SELF-COMPACTING LIGHTWEIGHT AGGREGATE CONCRETES Article Type: Research Paper Keywords: Expanded clay; Fiber reinforced concrete; Lightweight aggregate concrete; Self-compacting concrete; Recycled aggregate concrete. Corresponding Author: Dr. Valeria Corinaldesi, Ph.D. Corresponding Author's Institution: Università Politecnica delle Marche First Author: Valeria Corinaldesi, Ph.D. Order of Authors: Valeria Corinaldesi, Ph.D.; Giacomo Moriconi, Full Professor Abstract: In this work, fiber reinforced SCLWAC (self-compacting lightweight aggregate concrete) mixtures were studied, in which synthetic fibers were used. Eight different SCLWACs were prepared, in which, as aggregates, different combinations of fine and coarse expanded clay were tried, also partially replaced by either quartz sand or aggregate coming from concrete recycling. 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, and 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, while if the oven dry density of SCLWAC was lower than 1250 kg/m3 a strength class of LC 25/28 was reached as well. Tensile and flexural strength 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 was strongly improved by the addition of synthetic macrofibers, which provided strain-hardening effect similar to that achievable by means of steel fibres, even if characterized by a sensibly lower weight. In conclusion, SCLWACs showed excellent combination of mechanical and functional properties.

Cover Letter

Valeria CORINALDESI C.E., EngD. Permanent researcher position at the Department of Materials and Environment Engineering and Physics, Università Politecnica delle Marche Via Brecce Bianche, 12 60131 ANCONA, ITALY e-mail: [email protected] tel: +39 071 2204428 fax: +39 071 2204401 She is author and co-author of about 200 publications mainly on peer-reviewed international journals and conference proceedings. Main research interests: in general, these are mainly focused on the recycling of industrial by-products for the production of more sustainable and high performance construction materials. In particular, her main interests are centered on recycling rubble from building demolition as aggregates for structural concrete production.

Giacomo MORICONI Ch.E. Full Professor of Materials Science and Technology at the Università Politecnica delle Marche and Head of the Department of Materials and Environment Engineering and Physics, Via Brecce Bianche, 60131 ANCONA, ITALY e-mail: [email protected] tel: +39 071 2204725 fax: +39 071 2204401 He is the author of over 300 papers mostly in referred journals and symposia. His research is mainly developed in the area of materials engineering, with particular contributions to building materials performance and sustainable construction.

Highlights (for review)

RESEARCH HIGHLIGTHS   

Study and characterization of self-compacting lightweight aggregate concrete (SCLWAC) Use of lighter synthetic instead of steel fibers to obtain an improved post-cracking behaviour Design of special concretes with excellent combination of mechanical and functional properties

*Detailed Response to Reviewers

Reviewers' comments: Reviewer #3: The reviewer agrees with the improvements performed to the original paper and is satisfied with the answers and corrections; for that reason, the paper is recommended to accepted for publication.

Reviewer #4: This paper presents some properties of fiber reinforced SCLWAC (self-compacting lightweight aggregate concrete) mixtures incorporating synthetic fibers, recycled aggregate and expanded clay. Fresh and strength properties as well as dying shrinkage results are explained. This paper is revised by incorporating reviewer's comments. This paper will make good contributions to the existing knowledge and will be useful to the readers. However, the following comments are made: * State the mix design procedures - any standard design procedure followed. Discuss about the packing density of the mixes. Talk about the reproducibility of the mixes, especially dealing with the use of particular recycled aggregate of high density of 2.3. Explain about the feasibility of producing such complex SCLWAC mixes in practical production. Please explain why each of the components of the mix are used with potential benefits associated with each of them in terms of fresh, mechanical and durability properties. The mix design procedure adopted was that suggested for self compacting concrete mixtures (common practice based on Japanese extensive research results), that is based on considerations about the maximum volume of coarse aggregate particles (less than 340 l/m3), the suggested volume of very fine particles including cement (in the range 170-200 l/m3), volume of sand/volume of mortar about 0,5 and so on. If the recycled aggregate is made of only demolished concrete the mean value of 2.3 relative density is quite typical, the variations around this value are short, and not significantly higher than those detectable for natural aggregates. In practical production there are no differences with other self compacting concrete mixtures: obviously formworks should be water-tight, the casting should be preferably made from the bottom and so on. Each component of the mix has potential benefits, in particular: - Synthetic fibers are useful for counteracting concrete cracking, and consequently to rise concrete durability; - Expanded clay is useful for improving concrete lightness; - Superplasticizer is useful for improving workability at the fresh state; - Recycled aggregate is useful for reducing both environmental and economic impact of the mixtures; - Fly ash and silica fume are useful for assuring enough cohesiveness to the mixture without increasing the content of cement too much, moreover thanks to their pozzolanic activity they are able to improve concrete mechanical performance, finally their use is able to improve concrete durability due to their protective effect against sulphate attack, corrosion of reinforcement, alkali-silica reaction...

* Provide the air content of all SCLWAC mixtures. The air content of the mixtures has been reported as an additional raw in Table 1: EC+FA

EC+FA

+microF

+RCA

Air content 25

25

EC+FA +RCA+ macroF 20

EC+FA +sand 25

EC+FA

EC+FA

+sand+

+sand+

microF

macroF

25

20

EC+SF

EC+SF

+microF +macroF 25

20

* Durability can be a major issue with SCLWAC. As such, introduction of recycled aggregates to mix can be a problem. Why only drying shrinkage property test was conducted despite other durability test? Other durability properties can be included. As well known for SCLWAC the main problems of durability are related to drying shrinkage due to the low inert to cement ratio and the high content of very fine powders inside. For this reason the only drying shrinkage has been investigated in this paper, which was intentionally focused on mix design and mechanical aspects more than on durability. However, many papers reported in the scientific literature showed that for RAC dosage up to 20% by volume of concrete (as in this paper) no problems of durability occurred, neither in terms of aggressive agents penetration into concrete matrix (phenomenon that is mostly due to capillary interconnected voids of the cement paste) or in terms of freezing and thawing, alkali-silica reaction, internal sulphate attack and so on.

*Manuscript Click here to view linked References

USE OF SYNTHETIC FIBERS IN SELF-COMPACTING LIGHTWEIGHT AGGREGATE CONCRETES V. Corinaldesi*, G. Moriconi Università Politecnica delle Marche, Ancona, Italy *) corresponding author: Tel. +39 071 2204428, fax +39 071 2204401, e-mail [email protected]

Abstract In this work, fiber reinforced SCLWAC (self-compacting lightweight aggregate concrete) mixtures were studied, in which synthetic fibers were used. Eight different SCLWACs were prepared, in which, as aggregates, different combinations of fine and coarse expanded clay were tried, also partially replaced by either quartz sand or aggregate coming from concrete recycling. 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, and 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, while if the oven dry density of SCLWAC was lower than 1250 kg/m3 a strength class of LC 25/28 was reached as well. Tensile and flexural strength 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 was strongly improved by the addition of synthetic macrofibers, which provided strain-hardening effect similar to that achievable by means of steel fibres, even if characterized by a sensibly lower weight. In conclusion, SCLWACs showed excellent combination of mechanical and functional properties.

Key words: expanded clay, fiber reinforced concrete, lightweight aggregate concrete, selfcompacting concrete, recycled aggregate concrete.

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1. INTRODUCTION A great deal of experimental work has been reported and there are several examples of the use of self-compacting normal weight aggregate concrete. Recently, several studies have been published on the production and characterization of self-compacting lightweight aggregate concrete (SCLWAC) [1-6]. Some examples of SCLWAC application are related to bridge decks, repair work and strengthening of structural panels. The weight of concrete structures is quite large compared to the bearing loads, indeed. With the rapid development of very tall buildings, large-size and long-span concrete structures, structural lightweight concrete (LWAC) with different types of LWA has been widely investigated and successfully developed and used in recent years [7–13]. In fact, the application of structural lightweight concrete in the construction industry has many advantages, such as: high strength/weight ratio, savings in dead load for structural design and foundation, reduced risk of earthquake structural damage, superior heat and sound insulation characteristics, low coefficient of thermal expansion. Nevertheless, some limits in its engineering properties have prevented its widely use in the construction industry, as load bearing structural members. In particular, the brittleness of lightweight concrete is higher than normal weight concrete (NWC) for the same mix proportion and compressive strength [14]. Furthermore, generally, the mechanical properties of LWAC are lower than NWC, and if in general an increase in the concrete strength causes further brittleness of the concrete in compression and tension, this effect is especially evident in the case of LWAC [15]. One way to resolve the brittleness of LWAC can be the use of fibers. The literature on fiber reinforced LWAC shows that most of the research focused on the use of steel fibers, as single or combined with nonmetallic fibers [16-20]. Eight SCLWAC mixtures were prepared by using either fly ash of silica fume as mineral addition, and different combinations of aggregates with different specific weights, ranging from

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890 (fine expanded clay) to 2650 kg/m3 (sand), in order to obtain several density classes of concrete. In three mixtures, polypropylene microfibers were also added in order to prevent early concrete cracking, and preserve concrete durability. Moreover, in further three mixtures macrofibers were added in order to achieve an improvement of their post-cracking behaviour. Macrofibers are covered externally by a polypropylene reeded sheath, while their core is made of a glass fiber. All the SCLWACs were characterized both at the fresh and hardened state, in order to evaluate the influence on concrete performance of the various ingredients introduced in the mixture.

2. RESEARCH SIGNIFICANCE The objective of this research is to design a special concrete with excellent combination of performances, such as high strength and low weight, which are difficult to combine within the same concrete mixture (as enhanced by the state-of-the-art), as well as excellent fresh concrete workability and good post-cracking behaviour. For example, Mazaheripour, H, et al. [21] showed that SCLWACs could be obtained by using expanded clay, silica fume and polypropylene fibers (the same ingredients used in this work) with 28-day compressive strength in the range 24-26 MPa and density in the range 1800-2000 kg/m3. The main scope of this work was to obtained higher performance than those reported in [21] with mixtures characterized by lower unit weight. In particular, the goal was to achieve the highest concrete strength class as possible by means of SCLWACs with a dry oven density in the range 1200-1600 kg/m3. Moreover, an attempt was also made in order to reduce the cost (as well as to improve sustainability evaluable by means of life cycle assessment) of the mixture by using recycled aggregates from concrete demolition, partially replacing expanded clay. In fact, the expanded clay production requires rotary kilns and temperatures of about 1200°C, while recycled

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aggregate production just requires crushing of demolished material with low consumption of energy and raw materials saving. The field of application of this special concrete can be, first of all, that of reinforced concrete structures for seismic areas, where lightness, elasticity, easiness of concrete placing, and postcracking ductility are essential requirements for reducing costs, risks and damages.

3. PREPARATION OF CONCRETE SPECIMENS 3.1 Materials Portland cement type CEM I 52.5 R, according to EN-197/1, was used. The Blaine fineness of cement is 0.45 m2/g, while its relative specific gravity is 3.15. A low-calcium fly ash (ASTM C 618 Class F) produced by a thermal generating station was used as mineral addition besides to cement. The Blaine fineness of fly ash was 0.48 m 2/g and its relative specific gravity was 2.25. A silica fume obtained as a by-product of silicon wafer sawing during the production process of solar panels was used, as an alternative to fly ash. The BET fineness of silica fume was about 16 m2/g and its relative specific gravity was 2.21. As aggregate fraction, the heavier used was quartz sand (0-6 mm). Its relative specific gravity was 2.65 and its water absorption was equal to 1.5%. In addition, light expanded clay aggregates (either finer, 0-4 mm, or coarser, 0-15 mm in size) were used to decrease the overall weight of SCC. These aggregates are constructed from clay: they are produced in rotary kilns at temperatures of about 1200°C. The resulting produced aggregates are very lightweight, resulting of its internal spongy and porous structure. The relative specific gravity depends on their grain size of either 0.89 or 1.15 for the fine and coarse fraction, respectively, and they show high water absorption (15%) with respect to conventional aggregate.

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Partially replacing light expanded clay aggregates, a further lighter than natural aggregate was used: recycled concrete aggregate (0-15 mm). It comes from a recycling plant in which rubble from concrete structure demolition is suitably treated. Previous studies showed the feasibility of the use of recycled aggregates coming from the same plant for structural concrete production [22-24]. Its composition is 100% recycled concrete; the original concrete strength class was unknown and likely different for waste concrete coming from different sources. The main physical properties of the recycled aggregate fraction were relative specific gravity of 2.30 and water absorption of 8%. The grain size distribution curves of all the aggregate fractions are shown in Figure 1. As water reducing admixture, a 30% aqueous solution of carboxylic acrylic ester polymer was added to the mixtures. Finally, polypropylene microfibers (19 mm long, aspect ratio equal to 63) were added to some mixtures. Alternatively, synthetic reeded macrofibers were used, they were externally made by a polypropylene sheath with a corrugated surface, while their core is made of a glass fiber. Their length is 50 mm and their aspect ratio is equal to 110.

3.2 Concrete Mixture Proportions Eight different SCLWAC mixtures were prepared with the same kind of cement (CEM I 52.5 R), employed at a quite high dosage of 560 kg/m3. As mineral addition either fly ash (20% by weight of cement) or silica fume (12.5% by weight of cement), were adopted. Concerning the water reducing admixture, a dosage of either 1.4% or 1.6% by weight of cement was used, in the presence of fly ash and silica fume, respectively; the different dosage is due to the huge specific surface area of silica fume. Usually, the water to cement ratio adopted was equal to 0.42, but in the presence of polypropylene microfibers, due to their high specific surface area, the water

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content necessary to achieve the same workability level was higher, consequently the water to cement ratio increased up to 0.44. The SCLWACs mixture proportions are reported in Table 1. As aggregate, different combinations of quartz sand (0-6 mm), fine expanded clay (0-4 mm), coarse expanded clay (0-15 mm), as well as recycled aggregate (0-15 mm) were tried. The recycled-aggregate fraction was added to the mixture after water-soaking, in a condition very close to that defined as saturated surface-dried, as suggested in previous works [25]. The same procedure was followed for the expanded clay fractions. In order to meet the self-compactability requirement, firstly the two expanded clay fractions were suitably combined at 38% and 62% for the fine and coarse fractions, respectively. Then, expanded clay was partially replaced by recycled aggregate at the 28% by volume of the total aggregate (the dosage obviously has been corrected keeping into account the different volumic mass of the two kinds of aggregate). Finally, quartz sand was used, partially replacing both fine and coarse expanded clay fractions with a final proportion in volume of 17% fine expanded clay, 45% coarse expanded clay and 38% quartz sand. For all the texted mixtures the volume of coarse aggregate particles (those with size higher than 4 mm) is in the range 315-320 l/m3. In three mixtures, polypropylene microfibers (microF) were added at a suitable dosage (0.9 kg/m3) in order to prevent early concrete cracking (which can be expected on the basis of the high cement dosage employed: 560 kg/m3) and preserve concrete durability. Moreover, in further three mixtures synthetic macrofibers (macroF) were added at a dosage of 5,0 kg/m3.

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3.3 Preparation and curing of specimens Nine cubic specimens, 100 mm in size, were cast in steel forms for each concrete mixture for compression tests, and cured in sealed condition at 20°C. Further five identical specimens were prepared, and cured in the same way for splitting tension tests, as well as further three for dry oven density evaluation. Then, three prismatic specimens (100 by 100 by 500 mm) were prepared for each concrete mixture for 3-point bending tests, according to RILEM TC 162-TDF [26]. These specimens were cast in steel forms and cured in sealed condition at 20°C for 28 days. In the middle of the span (400 mm) the specimens were notched (the depth of the notch is 25 mm), see Figure 2. In addition, three cylindrical specimens, 300 mm high with a diameter of 100 mm, for each concrete mixture were manufactured for evaluating static modulus of elasticity in compression according to UNI 6556 [27]. Finally, further three prismatic specimens (100 by 100 by 500 mm) were prepared for each concrete mixture according to UNI 6555 [28] for drying shrinkage evaluation. After one day of curing in sealed condition, the specimens were stored at constant temperature (20±2 °C) and constant relative humidity (50±2%). After one days of curing in sealed condition, due to the high content of cement (see Table 1), the specimens prepared with the mixture ‘EC+FA+sand’ showed evident signs of early microcranking, likely due to autogenous shrinkage. In this mixture wasn’t added any fiber, indeed. The only other mixture without fibers is that called ‘EC+FA+RCA’, which didn’t show significant early-cracking. The reason could be a positive effect related to the use of pre-soaked porous recycled aggregates, able to act as internal water reservoir. The internal curing effect due to recycled aggregates with particle diameter in the range 4-8 mm (in this case the grain size distribution curve of the recycled aggregate used is 0-15 mm, so that including such range) has been already shown in previous works, in particular in [25].

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4. RESULTS AND DISCUSSION 4.1 Slump flow, V-funnel and L-box tests As a first step, properties of the fresh concrete other than slump were evaluated, according to EN 12350-8 [29], since in this case the slump value is not relevant due to very fluid concrete. Therefore, the attention was focused on the measurement of the slump flow, SF, which is the medium diameter of the slumped concrete. Also the elapsed time for the concrete to first touch the 500 mm circle (t500), as well as to reach the final configuration (tfin) was detected. Then, time elapsed for the SCCs passing through V-funnel was detected, according to EN 12350-9 [30]. Finally, in order to evaluate the filling capacity of highly congested structural members further tests were carried out by means of L-box with vertical steel bars, according to EN 12350-10 [31]. The difference in the concrete level between the beginning and the end of the box (passing ability ratio, PL, expressed in mm) and the elapsed time to establish the final configuration (tstop, expressed in s) were measured. Results obtained are reported in Table 2. Despite of some variability in the value of slump flow, all the mixtures can be considered self-compactable. Neither the presence of a halo of cement paste around the slumped concrete or the so-called ‘sombrero effect’ were observed. As shown in Table 2, the time elapsed for the SCCs passing through the V-funnel was found to be in the range 8–12 s in all cases, within the acceptance limits [30]. Also the results obtained by means of L-box are reported in Table 2. All concrete showed satisfactory, in some cases good, results in terms of mobility through narrow sections. Moreover, concerning with the flow-segregation, separation among coarse aggregate particles, fibers and the surrounding cement paste was never observed. By comparing the cohesive effect of the two different mineral addition, the use of silica fume even if at a lower dosage with respect to fly ash conferred higher viscosity to the concrete, with longer time to flow and slightly less passing

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ability. The same effect of silica fume on fresh concrete performance was given by the addition of fibers, particularly the macrofibers.

4.2 Dry oven density After 28 days of curing three cubic specimens for each mixture were oven dried at 105°C for 48 hours, then concrete dry oven density was evaluated and the values obtained are reported in Table 3. The density classes, also reported in Table 3, were indicated according to EN 206-1 [32]. As you can see, when the only expanded clay was used, a density class D 1.4 was obtained, and in particular the combined use of silica fume and expanded clay produced a particularly light concrete, with a dry density value in the range 1200-1250 kg/m3. On the other hand, by adding either natural sand or recycled concrete aggregate the density class D 1.6 was achieved, but by using recycled concrete aggregate lighter concretes were obtained, with a dry density value under 1500 kg/m3. The obtained oven dry density is very reduced, about 200 to 250 kg/m3, when compared with the fresh density (sum of mass dosages), when literature indicates that this reduction is usually inferior (100 to 200 Kg/m3) [33]. The reason likely is the use of fine LWA able to absorb much water.

4.3 Compression tests Compressive strength was evaluated up to 28 days of curing in sealed condition according to EN 12390-3 [34] on cubic specimens. The mean values obtained from three specimens for each curing time are reported in Table 4, as well as the corresponding strength class evaluated according to EN 206-1 [32].

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A strength class LC 25/28 was reached by those two mixtures showing a very low dry oven density value, under 1250 kg/m3 (see Table 3), thanks to the contribution of silica fume addition to the concrete strength development. On the other hand, at least a strength class LC 40/44 was achieved when quartz sand was combined with expanded clay, but the dry oven density value was in the range 1500-1600 kg/m3. In particular, even a strength class LC 45/50 was attained by the mixture containing quartz sand and randomly dispersed synthetic macrofibres. In fact, the macrofibers addition even if caused more viscous concrete didn’t compromise concrete degree of compaction (the mixture was still self-compactable), and the resulting compressive strength is about 10% higher than the same mixture without fibers. Generally, the same positive effect on compressive strength is achievable by using either steel fibers or synthetic fibers at high dosage [35]. Finally, by using recycled concrete aggregate an intermediate performance was obtained both in terms of compressive strength and density.

4.4 Static elastic modulus evaluation Static modulus of elasticity was determined in compression on cylindrical specimens according to Italian Standards UNI 6556 [27]. The mean values obtained after 28 days are reported in Table 5. With respect to the expected values of elastic modulus for structural normal weight concretes, on the basis of the formulas reported in the Building Codes, the values obtained for these SCLWAC are quite low. On the other hand, for lightweight concretes this other formula [36] can be more appropriate for predicting the value of elastic modulus:

E cm

f   22000   cm   10 

0.3

 E (1)

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where fcm is the mean value of the compressive strength evaluated on cylindrical specimens, while    E     2200 

2

(2)

where ρ = dry oven density, expressed in kg/m3. The values calculated by (1) are also reported in Table 5. Generally, the experimental values of the elastic modulus are slightly higher (plus 5÷10%) than those predictable from the formula (1), but this difference is particularly evident in the case of addition of macrofibers (+ 20÷30%). The reason for this 20-30% extra is likely attributable to the macrofiber composition: its sheath was made of polypropylene, while the core was made of a glass fiber. It is a sort of composite material itself. The presence of glass inside the fiber could be responsible for this higher elastic modulus. Moreover, macrofibers were used at high dosage (5 kg/m3 instead of only 0.9 kg/m3 for microF). In fact similar results were found by other authors [37] by using high volume of polypropylene fibers. The only mixture prepared with macrofibers and quartz sand (EC+FA+sand+macroF), that belonging to LC 45/50, was able to reach a value higher than 20 GPa.

4.5 Splitting tensile strength tests Tensile strength was evaluated according to EN 12390-6 [38] on cube specimens. The mean values of the first cracking stresses obtained from five specimens after 28 days are reported in Table 5. As expected, the addition of synthetic fibres did not significantly improve the maximum value of tensile strength.

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4.6 Three-point bending tests Flexural strength was evaluated according to RILEM TC 162-TDF [26] by calculating the tensile stress reached at the tip of the notch (25 mm depth), see Figure 2. The mean values of the first cracking stresses obtained after 28 days from three specimens are reported in Table 5. Also in this case, the addition of synthetic fibres did not significantly influence the value of firstcracking tensile strength. On the other hand, if the post-cracking behaviour is observed, a significant positive influence due to the addition of the PP macrofibers can be detected. In Figure 3 the curves obtained by means of the 3-point bending tests for the six mixtures containing fibers are shown. They represent the tensile stress reached at the tip of the notch as a function of the Crack Mouth Opening Displacement (CMOD, expressed in mm), measured by means of clip-gauge mounted on the mouth of the notch. In the presence of PP microfibres a softening post-cracking trend was observed, independently on the kind of aggregate used; while a significant strain-hardening after first-cracking was observed when PP macrofibers were added to the mixtures at a dosage of 5 kg/m3, corresponding to 0.55% by volume of concrete.

4.7 Drying shrinkage tests Drying shrinkage was evaluated up to at least 90 days according to UNI 6555 [28]. Results obtained are reported in Figure 4. The addition of PP microfibres, which showed to be useful for counteracting early autogenous shrinkage (the visual inspection of specimens did not detect microcracking), seems to increase drying shrinkage (see the mixtures represented by square symbols in Figure 3), probably because of their high specific surface area, leading to a slightly higher water to cement ratio (0.44 instead of 0.42), which was necessary for maintaining the same fresh concrete workability.

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When the recycled aggregate was used, the presence of a certain delay in the drying shrinkage development at early ages was noticed (compare the two mixtures represented by circle symbols in Figure 4). This delay can be attributable to the so-called curing effect, due to the use of presaturated porous aggregate particles (such as the recycled concrete particles), which are able to act as internal water reservoir as already outlined in §3.3 and in [25]). Also expanded clay was able to contribute to the internal curing effect, as widely reported in the literature [39-41], even if the combination between expanded clay and recycled aggregate particles appeared particularly effective (see Figure 4). However, concerning this last aspect, further investigation is needed. At longer ages this effect is no more present and the lower elastic modulus of recycled aggregates with respect to quartz sand produced higher deformation under exsiccation. Concerning the use of PP macrofibres (constituted by an internal glass fiber covered by PP layer), they seems to slightly reduce drying shrinkage (as it can be seen by comparing the mixtures represented by either circle or triangle symbols in Figure 4). This fact is consistent with the higher elastic modulus of the mixtures prepared by using this kind of fiber (+20-30%), likely due to both the higher elastic modulus conferred by the internal glass fiber with respect to the simply PP fibers, and the higher dosage (PP macrofibers were added at a dosage of 5 kg/m3 instead of only 0.9 kg/m3 for microF). The difference after 90 days of exposure to 50% R.H. are quite evident and the three mixtures prepared with macroF showed values of shrinkage in the range 0.1-0.2 mm/m, while those prepared with microF showed values in the range 0.3-0.4 mm/m. However, the positive influence of expanded clay in terms of internal curing (independently on the presence of recycled aggregate) is quite evident because the inert to cementitious materials ratio of all these mixtures is always extremely low (I/C in the range 0.69-1.05), and the expected values for their drying shrinkage after 90 days, in absence of internal curing, are well beyond 1.0 mm/m.

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5. CONCLUSIONS On the basis of the results obtained the following conclusions can be drawn:  In terms of fresh workability the self-compactability requirement was achieved for all the fiber reinforced LWACs, and, thanks to a quite viscous cement paste (due to the presence of mineral additions besides to cement), no signs of flow segregation was detected despite the use of very light ingredients such as expanded clay and synthetic fibers;  A minimum requirement of at least LC 25/28 strength class was achieved for all the tested mixtures (even for those belonging to D 1.4 density class), thanks to the addition of high amount of pure Portland cement, the high dosage of water-reducing admixture, and the use of mineral additions with evident pozzolanic activity;  A quite high strength class LC 45/50 was reached with a suitable combination of expanded clay, quartz sand and synthetic macrofibres, and this SCLWAC mixture was still rather light, belonging to D 1.6 density class;  Concerning mechanical properties other than compressive strength, the values of both first-cracking splitting tensile and flexural strengths were always consistent with concrete strength class; moreover, the post-cracking behavior of SCLWAC resulted strongly improved by the addition of synthetic macrofibers, which proved to guarantee a strainhardening effect similar to that achievable by means of steel fibres, even if characterized by a sensibly lower weight (and probably also by a less vulnerability to corrosion phenomena after opening of concrete cracks);  The only critical aspect could be the elastic modulus of SCLWAC, which were quite low with respect to normal weight SCC (coherently with the values expected for lightweight concretes, indeed); even if a certain improvement has been produced by the use of macrofibres (in fact, at least in the case of the mixture belonging to LC 45/50, a value of the elastic modulus higher than 20 GPa was achieved); it should be evaluated case by

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case if this low value of the concrete elastic modulus could be a problem for structural applications of SCLWAC elements;  By adding recycled concrete aggregate an intermediate performance was obtained with respect to the only expanded clay and the combination between expanded clay and quartz sand, both in terms of compressive strength and density;  In terms of drying shrinkage measurements, quite low values were detected in any case, thanks to the internal curing effect produced by both expanded clay and recycled aggregate particles; moreover, the addition of macrofibers seemed to be further effective in counteracting both early-concrete cracking due to autogenous shrinkage, and excessive strains due to drying shrinkage at longer ages;  In conclusion, the addition of synthetic macrofibers to SCLWAC allowed to design special concretes with excellent combination of performances, such as high strength and low weight, which are usually antithetic, as well as excellent fresh concrete workability, good stability under essiccation, and good post-cracking behaviour.

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17. Chen, B., Liu, J. (2005). Contribution of hybrid fibers on the properties of the high strength lightweight concrete having good workability. Cement and Concrete Research 35(5) 913–917. 18. Balaguru, P., Foden, A. (1996). Properties of fibre reinforced structural lightweight concrete. ACI Structural Journal 93(1), 62–77. 19. Perez-Pena, M., Mobasher, B. (1994). Mechanical properties of fiber reinforced lightweight concrete composites. Cement and Concrete Research 24(6), 1121–1132. 20. Hassanpour, M., Shafigh, P., Mahmud, H.B. (2012). Lightweight aggregate concrete fiber reinforcement – A review. Construction and Building Materials 37, 452–461. 21. Mazaheripour, H, Ghanbarpour, S., Mirmoradi, S.H., Hosseinpour, I. (2011). The effect of polypropylene fibers on the properties of fresh and hardened lightweight selfcompacting concrete. Construction and Building Materials 25 (1), 351-358. 22. Corinaldesi, V., Moriconi, G. (2009). Influence of mineral additions on the performance of 100% recycled aggregate concrete. Construction and Building Materials 23(8), 28692876. 23. Corinaldesi, V. (2010). Mechanical and elastic behaviour of concretes made of recycledconcrete coarse aggregates. Construction and Building Materials 24(9), 1616-1620. 24. Corinaldesi, V., Letelier, V., Moriconi, G. (2011). Behaviour of beam–column joints made of recycled-aggregate concrete under cyclic loading. Construction and Building Materials 25(4), 1877-1882. 25. Corinaldesi, V., Moriconi, G. (2010). Recycling of rubble from building demolition for low-shrinkage concretes. Waste Management 30(4), 655-659. 26. Vandewalle L. et al. (2003). RILEM TC162-TDF: Test and Design Methods for Steel Fibre Reinforced Concrete: sigma-epsilon design method (final recom-mendation). Materials and Structures 36(262), 560–567. 27. UNI 6556 (1976). Tests of concretes – determination of static modulus of elasticity in compression. 28. UNI 6555 (1973). Concrete made with aggregate maximum size 30 mm. Hydraulicshrinkage determination. 29. EN 12350-8 (2003). Testing fresh concrete - Part 8: Self-compacting concrete. Slumpflow test. 30. EN 12350-9 (2010). Testing fresh concrete - Part 9: Self-compacting concrete. V-funnel test.

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31. EN 12350-10 (2010). Testing fresh concrete - Part 10: Self-compacting concrete. L-box test. 32. EN 206-1 Concrete – Part 1: Specification, performance, production and conformity. 33. Lotfy, A., Hossain, K.M.A., Lachemi, M. (2014). Application of statistical models in proportioning lightweight self-consolidating concrete with expanded clay aggregates. Construction and Building Materials 65, 450–469. 34. EN 12390-3 (2003). Testing hardened concrete. Part 3: Compressive strength of test specimens. 35. Corinaldesi, V., Moriconi, G. (2011). Characterization of self-compacting concretes prepared with different fibers and mineral additions. Cement and Concrete Composites 33, 596 -601. 36. NTC 2008, Norme Tecniche per le costruzioni, D.M. 14/01/2008. 37. Kim, Y.J., Hu, J., Lee, S.J., You, B.H., Mechanical Properties of Fiber Reinforced Lightweight Concrete Containing Surfactant. Advances in Civil Engineering, V. 2010 (2010), Article ID 549642, 8 pages. 38. EN 12390-6 (2003). Testing hardened concrete. Part 6: Splitting tensile strength of test specimens. 39. Bentur, A., Igarashi, S., Kovler, K. (2001). Prevention of autogenous shrinkage in high strength concrete by internal curing using wet lightweight aggregates. Cement and Concrete Research 31(11), 1587–1591. 40. Lura, P. (2003). Autogenous Deformation and Internal Curing of Concrete, Ph.D. Thesis, Delft Institute of Technology, The Netherlands. 41. Costa, H, Júlio, E., Lourenço, J. (2012). New approach for shrinkage prediction of highstrength lightweight aggregate concrete. Construction and Building Materials 35, 84-91.

FIGURE CAPTIONS Figure 1 - Grain size distribution of the aggregate fractions. Figure 2 – Scheme of the 3-point bending tests (according to RILEM TC 162-TDF) and pictures of the clip-gauge mounted on the mouth of the notch. Figure 3 - Load vs. Crack Mouth Opening Displacement (CMOD). Figure 4 - Drying shrinkage vs. time of exposure to 50% R.H. and 20°C.

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Table 1

Table 1 – SCLWAC mixture proportions (kg/m3). EC+FA +microF

EC+FA +RCA

Cement 52.5 R Water Superplasticizer Fly Ash Silica Fume Expanded Clay (0-4 mm) Expanded Clay (0-15 mm) Recycled Concrete Aggregate (0-15) Quartz sand (0-6) PP microfibres

560 245 8 112 -

560 235 8 112 -

EC+FA +RCA+ macroF 560 235 8 112 -

226

100

367

Synthetic macrofibres 3

Air content (l/m )

560 235 8 112 -

EC+FA +sand+ microF 560 245 8 112 -

EC+FA +sand+ macroF 560 235 8 112 -

100

100

100

270

270

367

-

465

465

0.9

-

25

EC+FA +sand

EC+SF +microF

EC+SF +macroF

560 245 9 70

560 235 9 70

100

226

226

367

367

367

367

-

-

-

-

-

-

345 -

345 0.9

345 -

0.9

-

-

5.0

-

-

5.0

-

5.0

25

20

25

25

20

25

20

Table 2

Table 2 – Results of fresh SCLWAC testing. EC+FA EC+FA EC+FA EC+FA EC+SF EC+SF EC+FA EC+FA +RCA+ +sand+ +microF +RCA macroF +sand +sand+ microF macroF +microF +macroF 660 680 670 670 660 710 650 670 2 2 2 2 2 2 3 3 11 10 10 9 11 10 12 12

Slump flow test

SF (mm) t500 (s) tfin (sec)

V-funnel test

t (s)

8

7

10

8

7

9

10

12

L-box test

PL (mm) tstop (s)

75 18

70 16

90 20

75 15

80 18

90 19

85 21

110 22

Table 3

Table 3 – Oven dry densities and related density classes.

1320

1470

EC+FA +RCA+ macroF 1472

1.4

1.6

1.6

EC+FA EC+FA +microF +RCA Oven dry density (kg/m3) Density class, D

EC+FA +sand 1595

EC+FA +sand+ microF 1580

1.6

1.6

EC+FA EC+SF EC+SF +sand+ macroF +microF +macroF 1598 1231 1242

1.6

1.4

1.4

Table 4

Table 4 – Compressive strengths of SCLWACs (MPa). Days of EC+FA EC+FA EC+FA EC+FA curing +microF +RCA +RCA+ macroF +sand 1 26.3 31.5 31.7 34.3 7 34.2 39.6 41.0 47.6 28 44.7 49.0 46.7 52.1 Strength class, 30/33 35/38 35/38 40/44 LC

EC+FA +sand+ microF 33.4 47.2 54.5

EC+FA +sand+ macroF 37.8 44.1 58.7

EC+SF EC+SF +microF +macroF 33.5 36.0 37.8

37.0 38.2 40.3

40/44

45/50

25/28

25/28

Table 5

Table 5 – Results of SCLWACs testing after 28 days of curing. EC+FA EC+FA EC+FA EC+FA +microF +RCA +RCA+ macroF +sand 13.10 15.98 18.36 19.00

Static elastic modulus (GPa) Elastic 11.74 modulus from (1) Splitting 1.66 tensile strength (MPa) Flexural 2.96 strength (MPa)

EC+FA +sand+ microF 18.65

EC+FA EC+SF EC+SF +sand+ +microF +macroF macroF 23.31 10.19 13.60

14.96

14.75

18.05

17.85

18.71

9.69

10.04

2.25

1.99

1.76

1.90

2.19

1.70

2.33

2.84

3.47

2.64

2.64

3.00

2.00

2.11

Figure 1 Click here to download high resolution image


