1,721,017 research outputs found
Collapsible concrete as a blast and impact absorber: from material concept to static characterization
No full textIn this work a granular cementitious composite has been developed whose performance has to be characterized by low compressive strength and high deformation and energy dissipation capacity. This can be achieved by uniform grain size distribution, paste content as low as minimum theoretical void ratio and low paste strength, so to allow for energy dissipation after paste cracking due to both rearrangement of grain meso-structure and, in case, grain crushing. This study details the optimization of the material composition, in terms of w/c ratio, content of air entraining agent, mixing protocol, paste volume fraction, grain size distribution of the lightweight ceramic aggregate (LWA), and the static characterization
Behaviour of High Performance Fibre Reinforced Cementitious Composites under high dynamic loading and fire for safe tunnels
No full textIn this paper are described the results of an experimental study on the behavior of High Performance Fibre Reinforced Cementitious Composites under static and dynamic tension loading. This material has been developed for new segment tunnel resisting to fire and explosion. Results have shown the influence of the high temperature and the strain rate. The dynamic strength is increased by high temperature exposure, and the the toughness is progressively reduced. A change in the failure mechanism has been observed in dynamic increasing the exposure temperature
Dynamic tensile behaviour of high performance fibre reinforced cementitious composites after high temperature exposure
No full textThe uniaxial tension behaviour of high performance cementitious composites subjected to
high strain rates after high temperature exposure has never been investigated. The material
investigated was a steel fibre reinforced mortar. Straight low carbon steel micro-fibres
were used. The fibre content was 1.25% by volume and the mix design guaranteed a self
compacting mixture. The main purpose of the research was to highlight the role of thermal
damage in uniaxial tension at low and high strain rate loadings. Looking in particular at
peak strength and post-peak toughness the results show that, in low strain rate tests after
high temperature exposure up to 600 C, the thermal damage progressively reduces the
toughness and weakly increases the strength; at high strain rate the peak strength significantly
increases in comparison with low strain rate one for all the temperature investigated,
while the toughness for growing temperature progressively decreases
Tensile behaviour of high performance fibre-reinforced cementitious composites at high strain rates
Full text linkThe promise of fibre-reinforced cementitious composites for dynamic loading application stems from their observed good response under static loading. An experimental research aimed at contributing to the understanding of the behaviour of advanced fibre-reinforced cementitious composites subjected to low and high strain rates was carried out. The material behaviour was investigated at four strain rates (0.1, 1, 150 and 300 s -1) and the tests results were compared with their static behaviour. Tests at intermediate strain rates (0.1-1 s -1) were carried out by means of a hydro-pneumatic machine (HPM). High strain rates (150-300 s -1) were investigated by exploiting a Modified Hopkinson bar (MHB). Comparison between static and dynamic tests highlighted several relevant aspects. First, with the change in the strain rate, the Dynamic Increase Factor (DIF) of the material appears well predicted by some models proposed in the literature up to a value of 0.1 s -1, while at higher strain rates it increases less than expected from models. Moreover, the post-peak behaviour showed a stress plateau influenced by the fibres and dependent on the strain rate
Collapsible concrete: Un calcestruzzo ad alte prestazioni per la protezione di strutture da urti e impatti
No full textIn this work a granular cementitious composite
has been developed whose performance has to
be characterized by low compressive strength and
high deformation and energy dissipation capacity.
This can be achieved by uniform grain size
distribution, paste content as low as minimum
theoretical void ratio and low paste strength, so to
allow for energy dissipation after paste cracking
due to both rearrangement of grain mesostructure
and, in case, grain crushing. This study
detailsIn this work a granular cementitious composite
has been developed whose performance has to
be characterized by low compressive strength and
high deformation and energy dissipation capacity.
This can be achieved by uniform grain size
distribution, paste content as low as minimum
theoretical void ratio and low paste strength, so to
allow for energy dissipation after paste cracking
due to both rearrangement of grain mesostructure
and, in case, grain crushing. This study
details the optimization of the material
composition, in terms of w/c ratio, content of air
entraining agent, mixing protocol, paste volume
fraction, grain size distribution of the lightweight
clay aggregate (LWA), and the static
characterization.In this work a granular cementitious composite
has been developed whose performance has to
be characterized by low compressive strength and
high deformation and energy dissipation capacity.
This can be achieved by uniform grain size
distribution, paste content as low as minimum
theoretical void ratio and low paste strength, so to
allow for energy dissipation after paste cracking
due to both rearrangement of grain mesostructure
and, in case, grain crushing. This study
details the optimization of the material
composition, in terms of w/c ratio, content of air
entraining agent, mixing protocol, paste volume
fraction, grain size distribution of the lightweight
clay aggregate (LWA), and the static
characterization
“Collapsible” lightweight aggregate concrete. Part I: material concept and preliminary characterization under static loadings
No full textIn this work a granular cementitious
composite has been developed, tailoring its performance
to low compressive strength as well as to high deformation
and energy dissipation capacity. This peculiar
performance can be required to the material when
employed in post-installed screeds for protection of
structures and infrastructures against accidental actions
such as impact and blast. The required level of
performance can be achieved through uniform grain
size distribution, paste content as low as minimum
theoretical void ratio and low paste strength. It is
believed that the synergy between the aforementioned
three requirements can allow for energy dissipation
capacity after paste cracking due to both rearrangement
of grainmeso-structure and, in case, grain crushing.This
part I of a companion paper study first of all details the
optimization of the material composition, in terms of
mix-design variables such as w/c ratio, content of air
entraining agent, mixing protocol, paste volume fraction,
grain size distribution of the employed lightweight
expanded clay aggregate. The mechanical performance
of a trial collapsible concrete mix will be then checked.
In part II extensive mechanical characterization under
static and impact loadings will be performed as pertinent
to the intended aforementioned application
Behaviour of advanced cementitious composites under dynamic loadig and fire
No full textExplosions and fires in tunnel, potential hazards from highly-energetic materials stored in tanks and reservoirs
terroristic attacks are becoming safety issues. For such reason, the mechanical response of concrete structure subjected to impact loading and high temperature, main load conditions present in a blast scenario, cannot be ignored in the design, but they have to be predicted and controlled starting by investigation on proper material models for cementitious composites, and their response to strain-rate effects and thermal damage. The mechanical behaviour of cementitious composites when are subjected to extreme temperatures, impacts or blast has still many aspects open to investigation. As a matter of fact a scanty information provided so far by such special equipments
as the Hopkinson bar for very high strain rates (as in explosions) shows significant increases in peak strength, but these increases can provide a scanty information to design a structure subjected to a dynamic load. Moreover fibre cementitious composites are often used to improve the impact resistance, preventing scabbing and fragmentation problems, due to their ability in energy absorption, but the link between the dynamic energy and the static energy absorption, its strain rate sensitivity and thermal damage influence are not clear yet. In the paper some preliminary results on the behaviour of thermally damaged HPFRC subjected to high strain rate are presented and compared with results obtained in a static range
Dynamic Behaviour of UHPFRCC in Tension
No full textUltra High Performance Fiber Reinforced Cementitious Composites belong to a new class of structural materials characterized by high strength and ductility. Thanks to the high energy absorbed during the fracture process, due to multiple cracking and pull-out phenomena, they are often suggested for dynamic loading applications. Current understanding of the dynamic response is very limited because of very few investigations have been actually carried out. An experimental research aimed at contributing to the understanding of the behaviour of advanced fiber-reinforced cementitious composites subjected to low and high strain rates was carried out. The material investigated is a Ultra High Performance Fiber Reinforced Cementitious Composites. Straight high carbon steel micro-fibers were used. The material behaviour was investigated at several strain rates and the tests results were compared with their static behaviour. Tests at intermediate strain rates were carried out by means of a hydro-pneumatic machine (HPM), while high strain rates were investigated by exploiting a Split Hopkinson Tensile Bar (SHTB). A comparison between static and dynamic tests highlighted several relevant aspects regarding the influence of fibers on the peak strength and post-peak behaviour at high strain rates. Finally, this material will be employed in the construction of an innovative tunnel segment designed for extreme conditions (high temperature and shock)
On the influence of high temperature on the dynamic behaviour of High Performance Fibre Reinforced Cementitious Composites
No full text- …
