General Flashcards
CONCRETE - Chloride attack
1950s - 1970 used to speed up curing of concrete until banned in 1977. Additionally found in aggregate (sea dredged/unwashed.
Car parks exposed thermal variations, acidic rain, atmosphere co2, de-icing salts,
reduce alkali and passivity layer covering the reinforcements.
Remedy - remove source of water, treat reinforcement bars with a corrosion inhibitor.CONCRETE PATCH REPAIRS CAN CAUSE INCIPID ANODE AFFECT. Sacrificial Zinc Anodes. Cathodic protection via imposed current
CONCRETE - Carbonation
ELECTOR CHEMICAL PROCESS
Cracking in line with reinforcement bars
Concrete - Suphate Attack
Ambient water soluble sulphates. typically in in contaminated hardcore beneath. Permeate into LOW DENSITY CONCRETE.
Heave to concrete slab and displacement of masonry to perimeter. Progressive weakening of the slab leading to eventual failure.
DPM to be in stalled. Renewal of concrete and removal of contaminated hardcore.
High ALumina Cement HAC (1954 - 1976)
SEAWATER AND SULPAHTES in soil and groundwater.
1954-1976 PRE CAST PRE STRESSED concrete
beams Ability to cure quickly.
CONVERSION loss of strength. INCREASED POROSITY (CARBONATION) reduced resistance to CHEMICAL ATTACKS (Persistently damp areas).
VISUAL - Change of color light brown
Causes - HYDRATION forms CALCIUM ALUMINATES. Weaker cement matrix. Vulnerable to chemical attack.
CHEMCIAL TESTING —— STRUCTURAL ENGINEER (STRENGTH ASSESSMENT)
RESERVES of strength
HIGH TEMPERATURES INCREASED RISKS
ALKALI SILICA
Mapped (CRAZED ) cracking surface spalling and loss of strength. Sodium oxide equivalent scale in a chemical test to identify alkali content. CORE SAMPLES PETROMICROSCOPE OR POLISHED SECTIONS - XRAY MICROANALYSIS.
concrete cancer (ALKALI SILICA reaction)
reaction between high alkali cement paste and the reactive non-crystalline silica found in aggregate. Moisture leads to viscous gel reacting with aggregate causing it to expand.
R: Remove source of water.if localised renewal of area . Drying of structure and installation of membranes can pause evolution of the reaction. Some cases demolition is the only option.
