1,721,021 research outputs found
Engineering self healing capacity of cement based materials through crystalline admixtures
No full textIn this paper aims a thorough characterization will be performed of the effects of
crystalline admixtures, currently employed as porosity reducing admixtures, on the
self-healing capacity of the cementitious composites, i.e. their capacity to completely
or partially re-seal cracks and, in case, also exhibit recovery of mechanical properties.
The problem will be investigated with reference to both a Normal Strength Concrete
(NSC) and a High Performance Fiber Reinforced Cementitious Composite (HPFRCC).
In the latter case the influence of flow-induced fiber alignment will also be considered
in the experimental investigation. With reference to either 3-point (for NSC) or 4-point
(for HPFRCC) bending tests performed up to controlled crack opening and up to failure,
respectively before and after exposure/conditioning, the recovery of stiffness and
stress bearing capacity will be evaluated to assess the self-healing capacity. Moreover,
in a durability-based design framework, suitable self-healing indices to quantify the
recovery of mechanical properties will be defined
Reducing the Porosity and Sealing Cracks by Using Crystalline Admixture in Conventional Concrete
Get PDFThere is a continuous increase of quality on civil engineering materials in developed countries and parallel increase of need for new constructions in developing countries. Professional community should propose solutions for the durability that can resist in different severe environments. The most important factor that can affect concrete durability is represented by the pore distribution. Transport properties can take place through the porous network inside the cementitious composites and the aggregates interface, permitting the ingress of aggressive agents damaging concrete function intrinsically as a material and the well-functioning of the entire structure. The use of a crystalline admixture during the mixing procedure can fill the pores and capillarity of the cement composites, while in case of the appearance of the cracks, can perform as sealing agent, representing a secondary innovative benefit. Concrete structure, in this case will be more durable and there will be no need for un-planned interventio
On the use of crystalline admixtures in cement based construction materials: from porosity reducers to promoters of self healing
No full textThe project detailed in this paper aims at a thorough characterization of the effects of crystalline
admixtures, currently employed as porosity reducing admixtures, on the self-healing capacity of the
cementitious composites, i.e. their capacity to completely or partially re-seal cracks and, in case, also
exhibit recovery of mechanical properties. The problem has been investigated with reference to both
a normal strength concrete (NSC) and a high performance fibre reinforced cementitious composite
(HPFRCC). In the latter case, the influence of flow-induced fibre alignment has also been
considered in the experimental investigation. With reference to either 3-point (for NSC) or 4-point
(for HPFRCC) bending tests performed up to controlled crack opening and up to failure,
respectively before and after exposure/conditioning recovery of stiffness and stress bearing capacity
has been evaluated to assess the self-healing capacity. In a durability-based design framework, selfhealing
indices to quantify the recovery of mechanical properties will also be defined. In NSC,
crystalline admixtures are able to promote up to 60% of crack sealing even under exposure to open
air. In the case of HPFRCCs, which would already feature autogenous healing capacity because of
their peculiar mix compositions, the synergy between the dispersed fibre reinforcement and the
action of the crystalline admixture has resulted in a likely ‘chemical pre-stressing’ of the same
reinforcement, from which the recovery of mechanical performance of the material has greatly
benefited, up to levels even higher than the performance of the virgin un-cracked material
Autogenous healing on the recovery of mechanical performance of High Performance Fibre Reinforced Cementitious Composites (HPFRCCs): Part 2 – Correlation between healing of mechanical performance and crack sealing
Get PDFThis paper is the second part of a companion paper study focused on the autogenous self-healing capacity
of High Performance Fibre Reinforced Cementitious Composites (HPFRCCs). In part 1 investigation
has focused on the capacity of the material to completely or partially re-seal the cracks, as a function of
its composition, maximum crack width and exposure conditions. Different flow induced alignment of
fibres, with respect to the applied bending stresses have been also considered. The outcomes of the selfhealing
phenomenon, have been analyzed in terms of recovery of stiffness, strength and ductility, as
measured by means of 4-point bending tests, performed before (pre-cracking) and after the conditioning
exposure. In a durability-based design framework, self-healing indices quantifying the recovery of mechanical
properties were also defined and their significance cross-checked. In this paper the crack closure
will be evaluated, both through visual image analysis of the healed cracks as well as through a tailored
indirect method, proposed by the first authors in a previous study. This method is based on the
comparative analysis of the damage evolution curves built for both the pre-cracked and the healed stages
from the evaluation of the flexural stiffness. Recovery of mechanical properties will hence be correlated
to the identified amount of crack closure. In the authors' opinion, this step represents a fundamental
contribution in order to reliably and consistently incorporate the effects of self-healing into tailored
durability-based design approaches, based, e.g., on a “healable” crack width threshold concept
A “fracture testing” based approach to assess crack healing of concrete with and without crystalline admixtures
Get PDFIn this paper a methodology of characterization of both autogenic and engineered self-healing of ordinary concrete, with or without a crystalline admixture, has been assessed. The employed crystalline admixture consists of a mix of cement, sand and active silica and is added to the raw concrete constituents before mixing. The effects of the self healing phenomena on the recovery of stiffness and load-bearing capacity have been evaluated by means of 3-point bending tests performed up to controlled crack opening and up to failure, respectively before and after conditioning. Different exposure conditions have been considered, such as water immersion, air exposure and accelerated temperature cycles. Moreover, Ultrasonic Pulse Velocity tests and microstructural observations have been carried out. On the basis of the results, self-healing related indices have been also defined
High performance fiber reinforced cementitious composites: autogeneously self healing materials
No full text
- …
