Lecture #6 - Concrete Properties Flashcards
Define curing.
procedures used for promoting the hydration of cement and thus the development of the strength of the concrete
What does the curing procedure control?
temperature and moisture movement from and into concrete
Name some curing methods.
ponding, continuous sprinkling, absorptive mat, continuous wet fabric, steam curing
What is the objective of curing?
keep concrete saturated or as nearly saturated as possible until the originally water-filled space in the fresh cement paste has been occupied to a desired extent by the products of the hydration of cement
Which pores are responsible for reduction in strength and elasticity in concrete?
capillary pores and other larger pores
What effect does higher temperature have on curing?
rapid hydration, higher early strength, poor physical structure, non-uniform distribution of cement gel, lower long-term strength
What effect does lower temperature have on curing?
lower hydration which equals lower strength
Explain steam curing.
has objective of high early strength so you can do stuff faster, used mainly for precast concrete, applies in tunnels and specials chambers/portable boxes and plastic covers, can’t have a rapid temp rise
What are the primary factors affecting concrete strength?
water/cement ratio, compaction, age, temperature
What are the secondary factors affecting concrete strength?
aggregate/cement ratio, quality of aggregates, maxmimum size of aggregate, transition zone
What is microcracking?
very fine bond cracks between coarse aggregate and the hydrated cement paste becasue of the differential volume change between the cement paste and aggregates
How does the loading rate affect conrete strength?
fast increases the strength by about 20% and slow decreases the strength by about 20%
What is fatigue?
material failure mechanism due to cyclic/fluctuating stress
What governs fatigue resistance?
steel reinforcement in the reinforced concrete
Define creep.
increase in strain under sustained constant stress, delayed elastic deformation, happens when stress is held constant for some length of time
What happens when strain is held constant for some time?
stress decreases, referred to as relaxation
What is shrinkage?
loss of water in time and decrease in volume, caused by evaporation and hydration, affected by all parameters that contribute to water absorption and total void and also humidity and drying conditions
