Concrete & Formwork

Chapter 1. - Concrete as a Building Material, 1

Concrete Components, 1

Properties of Concrete, 1

Hardened Concrete, 2

Chapter 2. - Concrete Mix Components, 3

Natural Cement, 3

Portland Cement, 3

Water in the Mix, 5

Concrete Aggregate, 6

Handling Aggregate, 11

Concrete Admixtures, 13

Air-Entrained Concrete, 13

Other Admixtures, 16

Chapter 3. - Proportioning Concrete Mix, 17

The Book Method, 17

Trial Batch Method, 25

Absolute Volume Method, 29

Example of the Absolute Volume Method, 30

Variation in Mixes, 30

Chapter 4. - Excavation, 31

Soil Conditions, 31

Preliminary Considerations, 32

Sizing the Foundation, 33

Preparing Base for Slabs on Grade, 34

Fencing and Shoring, 34

Man Hours Required for Excavation, 37

Chapter 5. - Laying Out the Building, 38

Layout Procedure, 38

Chapter 6. - Design of Concrete Forms, 41

Design Considerations, 43

Design of Wall Forms, 43

Sample Wall Form Design Problems, 48

Columns Forms, 48

Sample Column Form Design Problem, 48

Foundation Forms, 50

Floor Forms, 50

Sample Floor Form Design Problem, 50

Stair Forms, 50

Chapter 7. - Form Materials and How to Use Them, 51

Lumber and Plywood, 51

Estimating Lumber Requirements, 51

Locating Wall Forms on a Footing, 52

Locating Footing Shoes and Studs, 53

How to Place Sheathing53

How to Place Walers, 53

General Principles, 54

Spreaders and Fasteners, 55

Anchor Bolts, 59

How to Install Anchor Bolts, 60

Anchor Bolts for Engine Beds and Steel Columns, 61

Construction Joints, 62

Expansion and Construction Joints, 63

Chapter 8. - Construction of Pier and Footing Forms, 66

Pier Footings, 67

Continuous Wall Footings, 68

Footing Forms, 68

Bonding a Wall to a Footing, 70

Building Pier and Footing Forms, 72

Steps in Making Small Pier Forms (Figure B-14) 72

How to Make Combination Footing and Pier Forms, 72

How to Make Individual Pier Footing Forms, 72

How to Make Stepped Footing Forms, 74

How to Make Tapered Footings, 74

How to Set and Brace Footing Forms, 75

How to Brace Stepped or Tapered Footing Forms, 76

How to Make and Set Forms for Wall Footings, 77

Chapter 9. - Construction of Foundation Wall Forms, 79

How to Make Panels for Single Wall Forms, 79

How to Nail the Sheathing, 81

How to Set the Forms on the Footings, 81

How to Make and Set Complete Single Wall Forms, 82

How to Make Panels for Double Wall Forms, 82

How to Make Complete Wall Forms, 83

How to Brace and Align Double Wall Forms, 84

How to Make Double Wall Forms With Cleated Panels, 86

Chapter 10. - Formwork for Openings in Concrete Walls, 87

How Openings in Concrete Walls are Formed, 87

How to Make a Box From, 88

How to Make Frames for Door or Window Openings, 89

How to Assemble the Frames, 90

How to Install the Frame in the Form, 91

Chapter 11. - Formwork for Steps, 92

Types of Concrete Steps, 92

Stair Riser Forms, 95

How to Make and Use a Pitch Board, 96

How to Install the Stringers, 98

How to Build Open Step Forms, 99

Chapter 12. - Formwork for Floor and Sidewalk Slabs, 102

How to Build a Form for a Section of Sidewalk 4 feet wide and 12 feet long, 102

How to Make Curved Sidewalk Forms, 103

How to Provide for Expansion Joints, 104

Chapter 13. - How to Make Beam and Girder Forms, 105

Chapter 14. - Forms for Arched Openings, 108

How to Build the Flat or Jack Arch Center, 109

How to Build a Segmental Arch Center, 110

How to Build the Semi-Circular Arch Center, 112

How to Set Arch Centers, 115

Chapter 15. - Handling and Placing Concrete, 117

Delivery Methods, 117

Placing Concrete, 119

Preliminary Preparation, 119

Depositing Concrete, 121

Consolidating Concrete, 124

Placing Concrete Under Water, 125

Chapter 16. - Finishing Concrete, 127

Repairing Concrete, 129

Cleaning Concrete, 129

Chapter 17. - Curing and Patching Concrete, 131

Curing Methods, 132

Removing Forms, 133

Patching, 134

Patching Old Concrete, 135

Chapter 18. - Effects of Temperature, 136

Hot Weather Concreting, 136

Cold Weather Concreting, 137

Chapter 19. - Reinforced Concrete Construction, 141

Characteristics of Concrete, 141

Reinforced Concrete Design, 142

Structural Members, 142

Shrinkage and Temperature Reinforcement, 144

Reinforcing Steel, 144

Splices, 147

Placement, 149

Chapter 20. - Precast Concrete, 151

Prefabrication Yard, 152

Chapter 21. - Cleaning Concrete and Masonry, 153

Methods, 153

Steam Cleaning, 153

Sandblast Cleaning, 154

Acids, Caustic Washers and Paste Cleaners, 155

Cleaning of Miscellaneous Stains, 156

Appendix A. - Method of Making Slump Test for Consistency of Portland Cement Concrete, 157

CHAPTER 1
CONCRETE AS A BUILDING MATERIAL

Portland cement is universally considered to be the most important masonry material used in modern construction. Its numerous advantages make it one of the most economical, versatile, and universally used construction materials available. It is commonly used for buildings, bridges, sewers, culverts, foundations, footings, piers, abutments, retaining walls, and pavements. A concrete structure, either plain or reinforced, is almost unique among the many systems of modern construction. In its plastic state concrete can be readily handled and placed in forms and cast into any desired shape. Quality concrete work produces structures which are lasting, pleasing in appearance, and require comparatively little maintenance.

Limitations. Recognition of the limitations of concrete construction in the design phase will eliminate some of the structural weaknesses that detract from the appearance and serviceability of concrete structures. Some of the principal limitations and disadvantages are:

(1) Low tensile strength. Concrete members which are subjected to tensile stress must be reinforced with steel bars, high-strength steel wire, or mesh.

(2) Drying shrinkage and moisture movements. Concrete, like all construction materials, contracts and expands under various conditions of moisture and/or temperature. This normal movement should be anticipated and provided for in the design, placement, and curing. Otherwise, damaging cracks may result.

(3) Permeability. Even the best concrete is not entirely impervious to moisture. It contains soluble compounds which may be leached out to varying degrees by water. Impermeability is particularly important in reinforced concrete where reliance is placed on the concrete cover to prevent rusting of the steel, and where the structure is exposed to freezing and thawing.

Chemical Process. The essential ingredients of concrete are cement and water which react chemically in a process called hydration to form another material having useful strength. Hardening of concrete is not the result of the drying of the mix, as can be seen from the fact that fresh concrete placed under water will harden despite its completely submerged state. The mixture of cement and water is called cement paste, but such a mixture, in large quantities, is prohibitively expensive for practical construction purposes and undergoes excessive shrinkage upon hardening.

Aggregates. Inert filler materials in the form of sand, stone, and gravel are added to cement and water in prescribed amounts to increase the volume of the mixture. When concrete is properly mixed each particle of aggregate is completely surrounded by paste and all spaces between aggregate particles are completely filled. The paste is the cementing medium that binds the aggregate particles into a solid mass.

Grout. Grout is a mixture of portland cement, lime, fine aggregate, and water in such proportions that the mixture is fluid. Exact proportions and the maximum size of the aggregate are dictated by the intended purpose.

Mortar. Mortar is a mixture of portland cement, lime, fine aggregate, and water in such proportions that the mixture is plastic. Exact proportions and the maximum size of the aggregate are determined by the intended purpose.

A plastic concrete is a concrete mix that is readily molded, yet changes its shape slowly if the mold is immediately removed. The degree of plasticity influences the quality and character of the finished product. Control of the ingredients in the mix limits the variables to the proportions of the ingredients. Significant changes in the mix proportions are indicated by the slump. The desirable qualities of plastic concrete are:

Workability. This property indicates the relative ease or difficulty of placing and consolidating concrete in the form. The consistency of the mixture is measured by the slump test (Appendix A) and is maintained as necessary to obtain the required workability for the specific conditions and method of placement. A very stiff mix would have little slump and would be very difficult to place in heavily reinforced sections. It is a good mix to place in a slab where reinforcing is not used. A more fluid mix can be placed where reinforcing steel is present. Workability is controlled largely by the amounts of and proportion of fine to course aggregate used with a given quantity of paste.

Nonsegregation. A plastic concrete should be handled so that there will be a minimum of segregation and the mix will remain homogeneous. For example, to prevent segregation, plastic concrete should not be allowed to drop (free fall) more than 3 to 5 feet. Care must also be taken in handling to prevent bleeding.

Uniformity. For uniformity every batch should be accurately proportioned according to the specifications. Uniform quality of the hardened concrete is desirable from both economic and strength considerations.

Hardened concrete in finished form is the actual basis of any concrete design. The essential qualities which must be considered are:

Strength. Strength is the ability of the concrete to resist a load in compression, flexure, or shear. The principal influencing factor on strength is the ratio of water to cement. About 2-1/2.) gallons of water are required for hydration (chemical reaction with water) of a sack of cement. Additional water is used to thin the paste, thus allowing it to coat more particles. This increases the yield obtainable from each sack of cement, thereby producing a more economical mix. However, excessive water-cement ratios should be avoided because thin paste is weak and a reduction in strength of the hardened concrete occurs due to the dilution of the paste. The minimum and maximum amounts of water generally used for economical mixes range from 4 to 8 gallons per sack.

Durability. Durability in concrete is the ability of the hardened mass to resist the effects of the elements, such as the action of wind, frost, snow, and ice, the chemical reaction of soils, or the effects of salts and abrasion. Durability is affected by climate and exposure. As the water-cement ratio is increased, the durability will decrease correspondingly. Air-entrained cements produce concretes with improved durability.

Water-Tightness. Water-tightness is an essential requirement of concrete. Tests show that the water-tightness of the paste is dependent on the amount of mixing water that is used and the extent to which the chemical reactions between cement and water have progressed. Frequently specifications for water-tightness limit the amount of water used in concrete mixes to 6 gallons per sack of cement. Water-tightness of air-entrained concrete is superior to that of non-air-entrained concrete.

Concrete & Formwork
by T.W. Love

All information you need to select and pour the right mix for the job, lay out the structure, select the right form materials, design and build the forms and finish and cure the concrete.

This is the new handbook for the concrete professional . . . the man on the job who needs sure answers to practical problems:

• What type of mix is best for the job
• What admixtures are needed
• How deep should the footing be
• What is the best way to lay out and design the forms
• How much concrete and form material are needed
• How can reinforcing and curing be handled most profitably

Nearly 100 pages of step-by-step instructions cover the actual construction and erecting of all forms in common use. Over 200 manhour tables, charts, and clear illustrations make this the most useful single volume with anyone working with site fabrication wood concrete forms.