USES AND CONSEQUENCES OF BUILDING MATERIALS · Mitigating some of the harmful effects ......
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USES AND CONSEQUENCES OF BUILDING MATERIALS – ATTAINING SUSTAINABILITY Marva Blankson PhD, MSc, BEng, P.E Associate Professor DIRECTOR CIVIL ENGINEERING DEPARTMENT F ACULTY OF ENGINEERING AND COMPUTING UNIVERSITY OF TECHNOLOGY , JAMAICA June 4, 2018
Transcript of USES AND CONSEQUENCES OF BUILDING MATERIALS · Mitigating some of the harmful effects ......
USES AND CONSEQUENCES OF BUILDING MATERIALS –
ATTAINING SUSTAINABILITYMarva Blankson PhD, MSc, BEng, P.E
Associate Professor
DIRECTOR
CIVIL ENGINEERING DEPARTMENT
FACULTY OF ENGINEERING AND COMPUTING
UNIVERSITY OF TECHNOLOGY, JAMAICA
June 4, 2018
Overview Introduction
Factors Influencing Deterioration
Mechanisms of deterioration
Local Experience with Deterioration
Traditional concrete
Development in Concrete Technology
Mineral admixtures in concrete
Self-consolidating concrete (SCC)
Corrosion Inhibiting SCC
Smart Concrete
Conclusion
Introduction
One of the glaring problems in the Jamaican built environment is the extensive deterioration of many of our structures that were built between 1940 and the late 1970s
This level of deterioration will make it difficult for the country to obtain the optimum stock of structures needed to support the minimum level of growth.
Introduction
The main reason for this lecture is to examine some of the durability-related issues with reinforced concrete structures from the pre 1970s era and to discuss development in materials and processes that may assist in
Mitigating some of the harmful effects
reducing maintenance activities,
extending the useful life of reinforced concrete structures
Better ensuring the best use of our natural resources
Factors Influencing Deterioration in Concrete Engineering and architectural details
Cover: The specified minimum concrete cover to reinforcement is predicated on the level exposure to destructive forces. Jamaican Building code, ACI 318
Cracks: Inevitable; but concerted effort should be made to minimise such. Many different types of crack. Curing, covering, providing joints
Quality of concrete: (cementitous materials content and type, type of aggregates) ASTM C150, C595 C1157
Environmental conditions: Chloride-laden atmosphere and environment with salt spray, high sulphate contents warrants special design consideration
Porosity: w/c ratio, level of compaction have effect on final quality. Permeation/diffusion of fluids that proves injurious to reinforced concrete can be minimised.
Delayed Ettringite FormationEtringite is usually formed early in the hydration process but high early temperatures in concrete can interfere with the normal reaction process (PCA). In such case, ettringite appears late in the hydration process and this results in expansion and cracking.
calcium sulfoaluminate (3CaO•Al2O3•3CaSO4•32H2O)
Corrosion
Corrosion is an electrochemical reaction1. Oxidation of iron. 𝐹𝑒 → 𝐹𝑒
2𝑒2. Conveyance of electrons through
the metal. 3. Reduction of oxygen 𝑂 + 2𝐻 𝑂 +
4𝑒 → 4𝑂𝐻_
4. The flow of current in the concrete pore solution is transported by ions from the anodic to cathodic region.
Progression of corrosion
Experience with Deterioration in Jamaica
Experience with Deterioration in Jamaica
Experience with Deterioration in Jamaica
Experience with Deterioration in Jamaica
Experience with Deterioration in Jamaica
Experience with Deterioration in Jamaica
Traditional Concrete
Traditional concrete is made with aggregate, sand, water and cement.
The reaction of cement
2 3𝐶𝑎𝑂. 𝑆𝑖𝑂 6𝐻 𝑂 → 3𝐶𝑎𝑂. 2𝑆𝑖𝑂 3𝐻 𝑂 3𝐶𝑎 𝑂𝐻 2 2𝐶𝑎𝑂. 𝑆𝑖𝑂 4𝐻 𝑂 → 3𝐶𝑎𝑂. 2𝑆𝑖𝑂 3𝐻 𝑂 𝐶𝑎 𝑂𝐻
Mineral Admixtures Ground granulated blast
furnace slag (GGBS), fly ash and silica fume have been used to replace various volumes of cements.
The use of these admixture helps to:
Reduce the penetrability of concrete
Increase the corrosion resistance of reinforced concrete.
Self-consolidating Concrete (SCC)
Concrete with considerable fluidity in the fresh state.
Constituents: cement, aggregates, water, mineral admixture and chemical admixture (high range water reducing agent)
Some of the mineral admixtures were described above.
Global Polycarboxylate Superplasticizer Market 2018 – Manufacturers, Product, Application, Regions by 2025
Interactions between Superplasticizer and Release Agents at the Concrete/Formwork Interface
SCC cont. - Durability
The transport system in SCC is minimised
Low permeability and surface absorption
Low diffusion
Refined microstructure
Low volume of cavities
Reduced connectivity between pores
Smaller pores
Improvement in the ITZ
The result is mitigation in penetration of injurious substances
Corrosion Inhibiting SCC This is self compacting concrete
with corrosion inhibitor.
Inherits all the improvements in properties that are manifested in SCC.
Offers even greater level of resistance to corrosion
This is very significant as not only penetration of deleterious substance is suppressed but any chloride ions that is diffused in the concrete is trapped.
This type of concrete has the potential to appreciably extent the life of concrete structure in marine environment.
Smart Concrete
Concrete that uses advanced technology to respond to its environment or provide real time information about the concrete.
It is therefore able to assist with structural health monitoring (SHM) or quality control.
Two types: Concrete with stress/strain sensors Concrete with carbon fibres
Concrete with stress and strain sensors
A sensor is inserted in the concrete to obtain real time data.
Enables acquisition of data on temperature
Provides information on strength development
Gives strength
Determines:
o Time for removal of forms
o Time to add/remove heat
o Assist with quality programme
Stress/strain sensor
Concrete with carbon nanofibresSmart concrete can be made by introducing carbon particles in the cementitious material.
Carbon is a conductive material.
Concrete is considered to be a poor conductor at best. However, this building material becomes conductive when incorporated with carbon particles.
The fibres do not need to made continuous contact in the concrete, the ubiquitous presence of the particles in the concrete charges the concrete and hence electrons can be transmitted through the concrete.
Concrete with 0.5- 1% carbon nanofibre is made to function as a smart material.
Carbon nano-fibres Carbon nanotube is made up of
carbon atoms bonded together.
Carbon Nanotubes are available as a single-walled hollow cylindrical (SWNT) material but there is also double-wall nanotubes (DWNT) that comprises two concentric layers of nanotubes There is also multiple-walled nanotubes (MWNT). This latter type is the favoured variety for use in composite materials.
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CM CT(0.5) CT(0.75) CT(1.0)
Strength (MPa)
Concrete with carbon nanofibres The conductivity of concrete with
carbon fibres changes under different conditions.
When compression load is applied, the fibres are brought closer together and the conductivity is increased.
Under tension load the fibres are pulled apart leading to cracking and hence conductivity is decreased.
With in the inclusion of the fibres, real time acquisition of data on the conductivity of the concrete is possible.
Information on initiation/development of cracks during a earthquake for example can be obtain.
Information used to establish immediate and effective maintenance of reinforced concrete facility.
Concrete with carbon fibres
Smart concrete has the potential to glean the following information in concrete:
Crack development
Permeability of water
Onset of corrosion
Electrical resistivity
Penetration of salts
Deformation
THE END OF PRESENTATION
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