Prefabricated timber-concrete composite floors
The presented investigation concerns the study of novel types of timber-concrete composite floors, manufactured with “dry connections” (Crocetti et al. In: 11th WCTE, Riva del Garda: international conference proceeding of 11th WCTE, Riva del Garda, 2010; In: RILEM 2013: Materials and Joints in Timber Structures—Recent Advancement of Technology Stuttgart, Germany, 2013: RILEM 2013, Stuttgart, 2013; Sartori et al. In: Enhance mechanical properties of timber, engineered wood products and timber structures. University of Bath, COST FP1004, Zagreb, 19 April 2012, 2012). Three full-scale nominally identical floor elements were investigated. The shear connector system used in the investigation was realized by means of self-tapping screws driven at an angle of 45° into the wood. First, the screws were inserted on the top of the glulam beams. Then, the beams were twisted upside-down and placed on concrete formwork (Fragiacomo In: Struct Eng Mech 20(2):173–189, 2005). Then fibre reinforced concrete (FRC) was cast in the formwork. Quasi-static bending tests and long-term bending test were performed. It was found that the proposed connection systems performed more than satisfactory in the short term, showing a very high degree of composite action even at load levels close to the failure load. However, long-term loading (Fragiacomo and Ceccotti In: J Struct Eng 132(1):13–22, 2006) induces increased deformation, which should be taken into account in SLS design.
An Innovative Prefabricated Timber-Concrete Composite System
A novel type of timber-concrete composite floor, consisting of longitudinal glulam beams with a fibre reinforced concrete (FRC) slab on the top is proposed. In order to check some relevant mechanical properties of such a floor, full-scale laboratory tests along with numerical analyses were carried out. The shear connector system used in the investigation consisted of self-tapping screws driven at an angle of 45° to the grain direction of the glulam beams. The manufacture of the structure occurred according to the following steps: (a) the screws were inserted on the top of the glulam beams; (b) the beams were rotated 180° about the longitudinal axis and placed in a concrete formwork; (c) the FRC was cast into the formwork; (d) after curing of the FRC, the composite floor was again rotated 180° about the longitudinal axis into its right position, i.e. with the FRC slab on the top side. Long term tests and quasi-static bending tests were performed. It was found that the proposed connection system showed a very high degree of composite action both during the long-term testing and at load levels close to the failure load. Furthermore, the assembly of the prefabricated timber-concrete composite system revealed to be very fast and easy.
Mechanical behaviour and durability of high volume fly ash cementitious composites
The purpose of this research is to separate different morphological particles of ASTM class F fly ash, and study their effect on mechanical behaviour and durability of high volume cementitious mixtures. In this research wet separation of raw fly ash is carried out, which resulted in three layers of different morphological particles. The first layer of particles float, comprise of about 1-5% of fly ash, is identified as cenospheres or hollow spheres. The second layer of particles is measured to be 55-60% of raw fly ash and consisting of porous spherical and rounded particles rich in Si and Al. The third layer particles is measured to be about 35-40% of raw fly ash. High volume fly ash cementitious composites containing second or third layer particles are tested under compression and bending, highlighting a higher strength and ductility in comparison to cementitious ones containing raw fly ash particles. KEYWORDS. Cementitious matrix; Raw fly ash; Second layer particles; Third layer particles.