CEEN 525 Exam II

Types of Common Deterioration

Types of Common Deterioration

delamination, vertical cracking, degradation

Rebar Corrosion

High alkalinity causes the formation of passive protective oxide film on surface. Chloride diffusion from salt causes results in the removal of of the film and development of corrosion products that can expand and cause damage.

Delamination

corrosion of rebar, delamination can extend over a substantial area and may not be visible to until it converts to spalling.

Vertical Cracking

plastic shrinkage, hydration heat, geometric constraints, traffic, freeze thaw and corrosion.

Infrared Thermography

-measuring the infrared radiation, the camera creates a map of the surface temperature

-In the case of defects, air/water will have different emission due to differences in thermal conductivity.

Impact Echo

strikes the object with an impactor that generates stress waves and using a fast, Fourier transform, the recorded signal is converted to the frequency domain. Peak frequency is identified.

-for a slab or intact member

Ultrasonic Pulse Echo

-transducer generates waves, which propagate through a medium.

-measures thickness with one-sided access.

-finding defects, debanding, delamination.

Downsides for Ultrasonic Pulse Echo

-perfect coupling required

-need of the close spacing of transducers, invisibility of fractures.

Sprayable Concrete

-mixture of cement, aggregate, water and admixtures project pneumatically from a nozzle.

-for tunnel support and mining.

-stabilization of slopes and walls

-concrete rehabilitation

-residential applications

Internal Curing

-fully pre-wetted lightweight aggregate is used as a moisture source for curing.

Steam Curing

-for accelerated strength gain (early)

- curing at atmospheric pressure with a curing cycle, including steps of delay, temperature, holding temperature and decrease in temperature.

Rebound Hammer Test (ASTM C805)

-tests surface hardness

-measures the rebound of a spring-loaded mass after it has struck a steel rod in contact with a smooth concrete surface.

Probe Penetration Test (ASTM C803)

-penetration of the probe using power-actuated gun, with measurements of the exposed length of the probe

-estimates compressive strength

Pullout Test (ASTM C900)

-casts the enlarged end of a steel insert into concrete.

-measuring the force to pull out of insert.

Pull-Off Test (ASTM C1538)

-tensile strength of concrete surfaces

-band strength by direct tension

-either evolution of concrete strength on the surface, or the band of an overlay branded to the concrete.

Ordering Concrete, Types

-Performance Based

-Prescription Based

-Combined option (performance and prescription)

Performance Based order

-compressive strength is defined prior to mixing

-producer selects materials and proportions to get the obtained strength

Prescription Based Order

-purchaser selects the mixture proportions, including cement, water, water-to-cement ratio and admixtures proportions

Combined Options

-purchaser designates compressive strength and minimum cement content.

- everything else is designated by the producer

Mixing Time

60s +15s of additional time for every additional cubic yard of concrete.

Three Methods of Mixing Concrete

-mixing in the central mixer

- shrink mixing: partially mixed in a stationary mixer, then in the truck.

-truck-mixed concrete

Concrete Curing

-the process of maintaining satisfactory moisture content and temperature in concrete for a sufficient period of time.

Curing Methods

-supplying additional moisture

-sealing the mix with the water

-accelerated curing

Ponding/Immersion (curing method)

-for laboratory curing or small projects

-excellent for when the temperature is above freezing but humidity is low

Issues with Ponding/Immersion (curing method)

-cost of sprinkling

-ample water supply

-need to prevent drying between watering intervals

Impervious Paper

-application and over-lapping of paper, wet surface of concrete can be cured

Membrane Forming Compound

-most widely used and practiced method

Mix Design

-the process by which performance characteristic of concrete defined

Mix Deign Characteristics

-strength

-water to cementitious material ratio

-aggregates

-air content

-slump

-water content

-cementing material content and type

-chemical admixtures

Levels of Exposure

-mild exposure

-not exposed to freezing and thawing and/or deicing agents

-moderate exposure

-severe exposure

Parameters for Concrete Mix Trial Batching

-required strength

-max water to cement ration or the minimum cementing

-nominal size of the aggregate

-air content

-desired slump

Probe Penetration

-probe is fired into surface of concrete with a KNOWN amount of force

-measures compressive strength

Pullout Test

-measures compressive strength, the force required to pull out metal insert.

-evaluation of concrete strength on the surface

Pull-Off Test

-measures tensile strength

-evaluation of concrete strength on the surface.

Fly Ash Class F

-decrease in early strength

-increase in late stage strength

-increase in workability

-increase in setting time, resulting in lower heat of hydration

Fly Ash Class C

-increase workability

-increase in long term strength

-decrease in permeability

-decrease to alkali-silica reactivity

Slag Cement

-80, 100, 120 grades

-delayed set time resulting in reduced heat of hydration

-decrease in early strength

-increase in later strength

Silica Fume

-increase in early strength (more than Fly Ash Type F)

-reduction in concrete bleeding/segregation

-resistance to sulfate environments

-increase in later strength

-increases water demand, because of its fine particle size

Compressive Strength Test

-6 in by 12 in specimen

-4 in by 8 in specimen allowed

-three samples total, two 6 in by 12 in, one 4 in by 8 in

Acceptance of Test Results (Compression)

-averages of three consecutive test remain above fc’ AND as long as no individual test is less than at least 500 psi of fc’ (fc’ < 5,000 psi), test is valid

-If individual test result is less than 0.10fc’ AND the averages of three consecutive tests remain above fc’ (fc’ > 5,000), test is valid

Acceptance of Test Results (Cores)

-averages of three cores remains is at least 0.85fc’ or greater

-single core should not be less than 0.75fc’

Fiber Reinforced Concrete

-increase in flexural strength

-more linear stress-strain behavior

-increase in compressive strength

-decrease in tensile strength

-no difference in modulus of elasticity

Dry-Mix Method

-cement and aggregate are batched on site, pressurized by compressed air and transported to a nozzle for application

-admixtures, water are added at nozzle

Wet-Mix Method

-cement, aggregate and water are batched and mix together prior to injection

-mixture is pneumatically and continuously projected into place

-air is added to increase speed of application, good compaction and aberrance.

Advantages of Wet-Mix Method

-less rebound

-less dust

-4~5 times higher application rate

-better assurance for water mixing with ingredients

-water to cement ratio can be low as 0.15

Sprayed Concrete Properties

-water to cement ratio = 0.4~0.5

-flow diameter = 22~24 inches

-3/8 in size aggregate

Split Tension Test

-measures tensile strength

-T=2P/(pi)*L*D

-cylindrical specimen subjected to compressive load along vertical diameter

Flexural Strength Test

-three loading point configuration

-R=(7.5-10)sqrt(fc’)

Steel Fiber Advantages

-increase the ductility of material

-increase flexural strength

-increased resistance against impact

-increased abrasion and erosion resistance

-increased water tightness and frost resistance

-increased bonding capacity compared to plain or mesh reinforced concrete