FUNDAMENTALS OF CONCRETE Presented By: Kevin J. Brigandi Construction Services Department Manager Debra A. Nunes Construction Services Department Manager

Uses of Concrete: Concrete can be formed in almost any color, shape and texture, while serving as an acoustic and thermal barrier Concrete can be placed in all environments and conditions Concrete is resistant to fire, chemical exposure and weather Concrete is environmentally safe and recyclable Concrete is efficient to construction and can be produced with a variety of durability characteristics and strengths CONCRETE BASICS

Dams, Roads, Bridges and Parking structures

Buildings

Retaining Walls, Foundations and Flatwork

Driveways and Sidewalks

Interior Flooring & Countertops

Controlled Low Strength Material (CLSM)

Insulated Concrete Forms (ICF’s)

What is Concrete?

Chemical Admixtures

Mineral Admixtures

How Should Concrete Be Specified?  Strength  Water / Cement Ratio  Air %  Minimum Cement Factor  Slump / Durability

Water / Cement Ratio Calculations 30 Gal 8.33 lb. 250 lb X = =.44 W/C 6 Sack 94 lb. 564 lb. 30 Gal 8.33 lb. 250 lb X = =.44 W/C 6 Sack 94 lb. 564 lb.

Adding Water to Concrete Water added (gal/yd³) Approx. Slump Increase (inches) Strength Reduction (psi) (%) % % % % % %

Entraining Air in Concrete / / / /8 5 79Less than 3/8 Mild Exposure Moderate Exposure Severe Exposure Nominal max size of aggregate, in.

Concrete Quality Control  All Field Technicians should be certified  And have a working knowledge of the following ASTM standards:  C31  C1064  C143  C172  C173  C231  C138

ASTM C 172: Standard Method for Sampling Freshly Mixed Concrete  Sample from middle portion of the batch  Sample at two or more regularly spaced intervals, not to exceed 15 min  Combine and remix sample thoroughly  Cover Sample to protect from drying

ASTM C 143: Standard Test Method for Slump of Portland Cement Concrete

ASTM C 231: Standard Test Method for Air Content of Freshly Mixed Concrete by the Pressure Method

ASTM C 173: Standard Test method for Air Content of Freshly Mixed Concrete by the Volumetric Method

Basic Techniques for Finishing Flatwork  Strike-off  Bull Floating  Darbying  Floating  Troweling  Brooming  Jointing  Edging  Curing

Finishing

Curing  Performed as soon as possible after final finishing is completed  Performed to prevent the loss of moisture from concrete  Helps in maintaining a favorable concrete temperature for a definite period of time  Will make concrete stronger –More impermeable –More resistant to stress –More resistant to abrasion –More resistant to freezing and thawing conditions

Curing Methods and Materials  Ponding or immersion  Spraying or Fogging  Wet Coverings  Impervious Paper  Plastic Sheets*  Membrane-Forming Curing Compounds  Steam  Insulating Blankets or Covers *discoloration can occur if not used properly

Common Concrete Problems Discoloration Dusting Cracking Plastic shrinkage cracking Crazing Scaling Curling Blisters Delamination Pop Outs

Discoloration

Prevention of Discoloration  Do not Use Calcium Chloride  Type, kind and condition of formwork  can influence color  Eliminate “Burning” of concrete  Proper curing - Caution with Plastic  Uniform sub-grade moisture

Powders under any type of traffic Easily scratched with a nail or even by sweeping Very weak wearing surface What is Dusting?

 Finishing operation performed while bleed water is on the surface or before bleeding has finished  Insufficient curing  Placement of non-absorptive sub grade or polyethylene vapor barrier  Floating/Troweling after the condensation of moisture from warm humid air is on cold concrete What Causes Dusting?

Prevention of Dusting  Do not place concrete directly on polyethylene vapor barriers or non- absorptive sub grades  Proper curing  Cold weather concrete practices  Vent exhaust to the outside to provide adequate ventilation

Cracking The one thing I can guarantee is that your concrete will crack!

Crazing

How To Prevent Crazing

How To Prevent Scaling

Repairing Scaled Concrete  Clean surface thoroughly  Resurface –Repair mortar –Portland Cement concrete

What Is Curling? The distortion of a slab into a curved shape due to temperature gradients throughout the depth of the concrete Slab Curling

Why Do Slabs Curl? Other Factors That Cause Curling: Bleeding / Poor curing / Joint spacing Shrinkage of the top relative to the bottom of the slab Moisture gradients in slab Temperature gradients within the slab

Minimization of Curling  Lowest practical slump  Largest practical aggregate size  Largest practical aggregate content  Avoid excessive bleeding  Avoid vapor barriers  Avoid higher than needed cement contents  Proper Curing  Adequate Joint spacing  Increase Slab Thickness

Blisters An irregular hollow bump that appears on the surface during or right after finishing operations

Why Does Concrete Blister?

How Do You Prevent Blisters?  Delay final finish as long as possible  Avoid surface drying  Initial float done with flat blades

 The top 1/8 inch of the surface is densified and separated from the base slab by a thin layer of air or water  Forms during final troweling  Most frequent in early spring and late fall Delaminations

What Are Pop Outs? A Conical Fragment that breaks out of the surface

Green Concrete Technology Benefits of Pervious Concrete  Environmental Benefits  Economic Benefits  Structural Benefits

Pervious Concrete Design

Mix Designs of Pervious Concrete  Supplementary cementitious materials (SCMs)  Coarse Aggregates  Water  Admixtures

Testing and Inspection of Pervious Concrete  Density Testing (ASTM C29)  No Slump  No Air

Self Consolidating Concrete  The use of self-consolidating concrete (SCC) has grown tremendously since its inception in the 1980s.  Because of the material performance in its fresh state, the existing testing methods for conventional concrete are no longer suitable for SCC.

Mix Designs for SCC  SCC mixtures can be designed to provide the required hardened concrete properties for an application, similar to regular concrete.

Benefits of Self Consolidating Concrete  Improved constructability  Virtually flawless finish  Homogenous and uniform concrete  Better reinforcement bonding  Flows easily into complex shapes and through congested reinforcement  Superior strength and durability  Allows for innovative architectural features

Benefits of SCC  Wall with Normal and SCC Concrete

Testing Procedures for SCC

The Industry Reference

Contributions By: The Portland Cement Association The American Concrete Institute The National Ready-Mix Concrete Association Blue Circle Cement St. Lawrence Cement Connecticut Concrete Promotion Council The Portland Cement Association The American Concrete Institute The National Ready-Mix Concrete Association Blue Circle Cement St. Lawrence Cement Connecticut Concrete Promotion Council