Concrete Production and Construction Methods

Introduction and Context

Concrete is a manufactured composite material whose performance depends not only on cement, water, aggregates, and admixtures, but also on production control and construction practice. A well-designed mix can fail when batching is inaccurate, transport causes segregation, placement is delayed, vibration is inadequate, formwork moves, reinforcement is displaced, or curing is neglected. Concrete construction is therefore a connected production system extending from material storage to acceptance testing and service performance.

This chapter examines the planning and control of batching, mixing, transport, pumping, placement, consolidation, finishing, curing, formwork, falsework, reinforcement, precasting, prestressing, testing, and quality assurance. The emphasis is on selecting methods that are technically suitable, safe, economical, environmentally responsible, and compatible with project constraints.

Learning Objectives

After studying this chapter, students should be able to:

1. Explain the relationship between concrete materials, mix proportions, production, and performance.
2. Plan batching, mixing, transport, pumping, placement, consolidation, finishing, and curing operations.
3. Select suitable formwork, falsework, reinforcement, precasting, and prestressing methods.
4. Calculate basic production quantities, yield, productivity, and water–cement ratio.
5. Interpret fresh- and hardened-concrete tests and develop a quality-control plan.
6. Identify construction defects, their causes, and appropriate preventive measures.
7. Evaluate a concrete operation using safety, sustainability, cost, and constructability criteria.

1. Concrete as a Controlled Construction Process

Concrete consists principally of cement paste, fine aggregate, coarse aggregate, water, and, where required, chemical or mineral admixtures. Cement reacts chemically with water through hydration. The paste binds the aggregates, while the aggregate skeleton provides volume stability and reduces cost. Concrete is strong in compression but comparatively weak in tension; reinforcement or prestressing is therefore used when tensile stresses are significant.

The main variables affecting performance are:

• water–cementitious-material ratio;
• cementitious-material type and content;
• aggregate grading, shape, moisture, and cleanliness;
• admixture dosage and compatibility;
• mixing energy and duration;
• time and temperature between mixing and placement;
• compaction, curing, and protection; and
• quality of formwork and reinforcement installation.

A construction method must preserve the intended properties through every stage. For example, adding water at the site may increase slump but also increase the water–cement ratio and reduce strength and durability. A responsible response is to use an approved water-reducing admixture or revise the mixture under controlled procedures.

Important terminology

• Batching: Measuring concrete ingredients for one load or batch.
• Mixing: Combining ingredients to achieve uniform distribution.
• Slump: A field measure of the consistency and workability of fresh concrete.
• Segregation: Separation of coarse aggregate from mortar or paste.
• Bleeding: Upward movement of water to the surface of freshly placed concrete.
• Consolidation: Removal of entrapped air and improvement of contact with reinforcement and forms.
• Cold joint: A discontinuity caused when a new layer is placed after the previous layer has lost adequate plasticity.
• Honeycombing: Voids or exposed coarse aggregate caused by inadequate mortar or consolidation.
• Curing: Actions that maintain moisture and temperature conditions for hydration and strength development.
• Falsework: Temporary structural support for formwork, fresh concrete, or construction loads.

2. Mix Proportioning and Batching

Concrete proportioning seeks a mixture that satisfies strength, durability, workability, placing, and economy requirements. The required strength is normally higher than the specified characteristic strength because production has variability. The mix designer considers exposure class, maximum aggregate size, cementitious materials, air content, slump, placing method, and required early-age strength.

The water–cement ratio is a central durability and strength-control parameter:

where m_w is the mass of water and m_c is the mass of cement, both in the same units, usually kilograms. For blended binders, the water–cementitious-material ratio may be used:

where m_cm is the total mass of cementitious materials. These ratios are mass ratios, not volume ratios. They are applicable when the specified mixture and materials are known; they do not alone predict strength because curing, cement type, air content, age, and testing also influence performance.

Worked example. A batch contains 180 kg of water and 360 kg of cement. The water–cement ratio is:

If 40 kg of supplementary cementitious material is included and the specification uses w/cm, then:

Batching may be by mass or, for limited low-risk work, by controlled volume. Mass batching is preferred because aggregate moisture and bulk density make volume batching less reliable. Moisture corrections are essential. Wet aggregate contributes water to the mix; dry aggregate absorbs part of the mixing water. The batch plant should therefore measure aggregate moisture regularly and adjust both aggregate mass and added water.

A simple production-yield check is:

where Y is the yield ratio, V_actual is the measured volume produced, and V_theoretical is the sum of ingredient absolute volumes. A yield near 1.00 is expected, subject to the governing specification and measurement accuracy.

Batching systems should include calibrated weighing equipment, separate aggregate bins, cement and admixture dispensers, water meters, interlocks, and batch records. The operator should verify material identification, scale zero, aggregate moisture, batch size, and admixture dosage before production.

3. Mixing and Production Equipment

Mixers may be stationary, truck-mounted, or continuous. Stationary mixers are common at central plants and precast facilities. Truck mixers transport and agitate concrete and may complete mixing on site. Continuous mixers are useful for certain high-volume or controlled applications but require careful feed-rate control.

Mixing time is not a universal fixed value. It depends on mixer type, batch size, material characteristics, and the governing standard. The correct criterion is uniformity, demonstrated by the relevant specification or plant qualification procedure. Excessive mixing can increase temperature, entrained-air loss, or wear, while insufficient mixing produces nonuniform batches.

A typical sequence is to introduce part of the mixing water, coarse aggregate, fine aggregate, cementitious materials, remaining water, and admixtures according to the approved method. The sequence must be compatible with the admixture supplier’s instructions. Admixtures should not be casually combined because incompatibility may cause rapid stiffening, excessive air, delayed setting, or segregation.

Production capacity can be estimated from batch volume and cycle time:

where Q is theoretical production rate in m³/h, V_b is batch volume in m³, and t_c is total cycle time in minutes. Actual output is lower when loading delays, truck queues, maintenance, testing, and interruptions are included. A plant producing 2.0 m³ per batch with a 6-minute cycle has a theoretical rate of 20 m³/h, but scheduling should use a lower practical rate.

4. Transport, Pumping, and Placement

Transport must preserve uniformity and workability. Common methods include wheelbarrows, buckets, skips, cranes, conveyors, chutes, truck mixers, and pumps. Selection depends on volume, height, distance, access, reinforcement density, required rate, and site congestion.

Concrete should not be dropped from excessive heights or moved horizontally over long distances without control, because these actions encourage segregation. Chutes should have suitable slope and should not contain abrupt changes that cause separation. Concrete delivery should be coordinated with placing crews so that trucks do not wait excessively and successive layers can be joined properly.

Pumping is effective for high-rise, congested, or large-volume work. Pump selection considers required discharge, vertical and horizontal pipeline length, bends, pressure, aggregate size, slump, paste content, and temperature. Before pumping, the line is normally lubricated with a suitable grout or mortar that is handled according to the approved method; contaminated or poorly proportioned priming material must not be incorporated without authorization. Pipeline supports must resist movement, and workers must remain clear of pressurized couplings.

Placement should proceed in planned lifts or layers. The placing rate must be compatible with formwork pressure, consolidation capacity, finishing requirements, and the time available before setting. Concrete should be deposited as close as practicable to its final position. Rehandling is minimized, and the placement plan identifies construction joints, emergency stoppage procedures, lighting, access, and standby equipment.

5. Consolidation, Finishing, and Curing

Consolidation removes entrapped air and ensures that concrete surrounds reinforcement and fills the forms. Internal vibrators are the most common method. The vibrator is inserted vertically at regular spacing, allowed to penetrate the previous layer sufficiently to knit layers, and withdrawn slowly. It should not be used to transport concrete over long distances. Over-vibration can cause segregation, loss of entrained air, or formwork damage; under-vibration causes honeycombing and weak interfaces.

External vibration, vibrating tables, surface vibrators, and self-consolidating concrete are alternatives. Self-consolidating concrete requires careful control of viscosity, flow, segregation resistance, formwork pressure, and placement sequence.

Finishing begins only when the surface condition is suitable. Premature finishing can trap bleed water and create a weak, dusty surface. Typical operations include screeding, bull floating, edging, joint tooling, power trowelling, brooming, and curing-compound application. The specified texture must match the intended use and slip-resistance requirements.

Curing maintains moisture and temperature so hydration can continue. Methods include water curing, wet coverings, plastic sheeting, curing compounds, internal curing, and insulated protection. Curing begins as soon as finishing and surface condition permit. Hot, dry, windy conditions increase evaporation and plastic-shrinkage risk; cold conditions slow strength development and may cause freezing damage.

A useful evaporation-risk concept is that the rate of surface water loss rises with high concrete temperature, high air temperature, low relative humidity, and wind. Exact prediction should use an accepted standard or project procedure rather than an informal rule. Preventive measures include windbreaks, shading, fogging, cooling materials, evaporation reducers where approved, timely curing, and adjusted placing times.

6. Formwork and Falsework

Formwork gives concrete its shape, supports fresh-concrete pressure, and provides the required surface finish. It may be timber, plywood, steel, aluminum, plastic, stay-in-place material, or a proprietary system. Design and planning address strength, stiffness, stability, dimensional accuracy, leakage, release agents, reuse, stripping sequence, and access.

Fresh concrete pressure depends on placement rate, temperature, slump, setting characteristics, member geometry, and vibration. Formwork must be designed for lateral pressure, vertical loads, construction live loads, impact, wind, and accidental effects as required by the applicable code. Connections and ties must be adequate; local panel strength alone is not sufficient.

Falsework supports formwork and sometimes partially hardened concrete. It must have a complete load path to competent ground or the permanent structure. Sole plates, jacks, bracing, joints, and foundations require inspection. Differential settlement can produce cracking, dimensional errors, or collapse. A temporary works design should identify design assumptions, erection sequence, inspection hold points, and removal criteria.

Before placement, inspect dimensions, line, level, cleanliness, tightness, release agent, embedded items, openings, construction joints, and access. Stripping must not occur merely because the surface appears hard. Required in-place strength, member span, load condition, temperature history, and engineer approval govern removal. Reshoring may be necessary when upper-floor construction loads are transferred to lower floors.

7. Reinforcement Installation

Reinforcement must be correctly sized, spaced, shaped, supported, lapped, anchored, and protected by specified concrete cover. The drawing and bar-bending schedule control installation. Bars should be clean and free from loose rust, oil, mud, or coatings that impair bond.

Chairs, spacers, bolsters, and tying wire maintain position during placement. Supports must be strong enough to withstand worker movement and vibration. Reinforcement should not be displaced by walking, pump hoses, or vibrators. Congested reinforcement requires a constructability review because theoretical bar arrangements may prevent concrete flow and consolidation.

Lap lengths, development lengths, hooks, mechanical couplers, and welding must comply with the structural design and governing standard. Cover is measured to the specified surface of reinforcement and is essential for durability and fire resistance. Field modifications, such as cutting bars to accommodate services, require design authorization.

A reinforcement inspection should verify bar mark, diameter, quantity, spacing, location, lap, anchorage, cover, support, cleanliness, embedded items, and access for concrete placement. Inspection should be completed before closing forms.

8. Precast and Prestressed Concrete

Precast concrete is manufactured away from its final position in a controlled plant or casting yard. Benefits include repeatable quality, reduced site labor, rapid erection, improved finish, and reduced formwork at the site. Constraints include transportation limits, lifting points, tolerances, connection design, storage, erection stability, and crane access.

Precast production normally includes mould preparation, reinforcement and inserts, concrete placement, consolidation, curing, demoulding, inspection, storage, transport, and erection. Dimensional tolerances and connection details must be established early because small errors can accumulate across repeated units.

Prestressed concrete introduces a deliberate compressive force to reduce tensile stress under service loading. In pre-tensioning, strands are stressed against external abutments before concrete is cast; force is transferred after concrete reaches the specified release strength. In post-tensioning, ducts or sheaths are placed in hardened concrete, tendons are stressed with jacks, and the tendons are anchored; bonded systems are subsequently grouted when required.

The effective prestress is less than the initial force because of elastic shortening, anchorage slip, friction, relaxation, creep, and shrinkage. A simplified force relationship is:

where P is tendon force in newtons, σ is tendon stress in pascals, and A_p is tendon area in square metres. This equation applies to a uniform tendon stress state and does not by itself account for losses. Design calculations must use the applicable prestressed-concrete code.

Prestressing operations are high-risk. The exclusion zone behind anchorages, calibrated jacks, tendon identification, stressing sequence, elongation records, grout quality, venting, and corrosion protection require strict control. Workers must never stand in line with an active tendon or anchorage.

9. Testing and Quality Control

Quality assurance is the planned system that provides confidence that requirements will be met. Quality control is the operational inspection and testing used to verify conformity. A project quality plan should define responsibilities, approved materials, inspection and test plans, hold points, sampling, acceptance criteria, records, nonconformance procedures, and traceability.

Fresh-concrete tests

Common tests include temperature, slump or slump flow, air content, density, unit weight, visual uniformity, and sampling for strength specimens. Slump is useful for consistency but is not a direct measure of strength. A high slump may result from high water content, a water reducer, or a self-consolidating mixture; interpretation requires knowledge of the mixture.

Fresh-concrete density may be estimated by:

where ρ is density in kg/m³, m is the measured mass in kilograms, and V is the container volume in cubic metres. The container must be calibrated and filled according to the relevant test method.

Hardened-concrete tests

Compressive-strength specimens are tested at specified ages using standardized procedures. The nominal compressive stress is:

where f_c is compressive strength in pascals or megapascals, P is maximum applied load in newtons, and A is loaded cross-sectional area in square metres. The specimen geometry, end condition, curing, loading rate, and test standard affect the result.

Strength acceptance is generally based on a statistical series rather than one isolated result. Mean strength is:

where x_i are individual results and n is the number of results. Sample standard deviation is:

These statistics describe production variability; they do not replace the acceptance rules of the governing code. A low result should trigger investigation of sampling, curing, testing, batching, placement, and in-place conditions before conclusions are made.

Other tests include flexural strength, splitting tensile strength, modulus of elasticity, permeability indicators, rapid chloride-ion tests, absorption, maturity, rebound hammer, ultrasonic pulse velocity, and cores. Non-destructive tests are valuable for screening and uniformity but often require correlation with reliable project-specific data.

10. Integrated Quality-Control Planning

A practical inspection and test plan links each activity to a risk, control, responsible person, record, and acceptance criterion. Examples include:

Nonconforming concrete should be identified, segregated where possible, and assessed by competent personnel. Disposition may involve acceptance, repair, strengthening, additional testing, removal and replacement, or engineering analysis. Concealing a defect or altering test records is unacceptable and can create structural, legal, and ethical consequences.

11. Safety, Sustainability, and Professional Responsibility

Concrete work involves rotating machinery, reversing trucks, suspended loads, pressurized pump lines, cement burns, silica-containing dust, noise, vibration, falls, and collapse hazards. Controls include exclusion zones, traffic management, personal protective equipment, safe hose handling, lockout procedures, wash stations, formwork inspections, lifting plans, and competent supervision. Wet cement can cause severe skin and eye injury; waterproof gloves, boots, long sleeves, eye protection, and prompt washing are necessary.

Concrete production has significant embodied carbon, principally associated with cement manufacture. Lower-impact strategies include optimized structural design, reduced over-ordering, supplementary cementitious materials where technically suitable, recycled aggregate where permitted, local sourcing, efficient transport, reusable formwork, recovery of wash water under controlled conditions, and accurate quantity planning. Sustainability must not compromise durability, fire performance, constructability, or service life.

Digital batch records, sensors, truck tracking, maturity monitoring, three-dimensional coordination, and automated inspection can improve traceability. Artificial intelligence may assist anomaly detection, production forecasting, and image-based defect classification, but it cannot replace engineering judgment, calibrated testing, code compliance, or accountable decisions. Data governance must address calibration, cybersecurity, privacy, model bias, and auditability.

12. Applied Case: Illustrative High-Rise Floor Slab Pour

Background

A contractor must place 420 m³ of reinforced-concrete floor slab in a high-rise building. The slab contains congested reinforcement around columns. Concrete is supplied from a central plant 18 km away and pumped through a boom pump. The specified slump range is 150–190 mm, and the placement must be completed during one planned shift.

Problem

A preliminary schedule based only on truck capacity predicts completion in 10 hours. However, the site has limited truck access, two narrow pump-line sections, and forecast hot, windy weather. The risks are delivery interruption, loss of workability, cold joints, rapid evaporation, and excessive formwork pressure.

Analysis

The contractor reviews plant capacity, travel time, truck turnaround, pump output, standby equipment, reinforcement access, and the allowable placing rate. The practical supply rate is estimated at 45 m³/h, although the plant’s theoretical capacity is higher. At this rate, the nominal placing time is:

The schedule must also allow setup, testing, truck variation, planned breaks, and contingency. The team therefore proposes an earlier start, a second approved supply route, a standby pump, and a controlled emergency construction-joint location.

Approach and solution

Before the pour, the team:

1. verifies mix approval, aggregate moisture, admixture compatibility, and plant calibration;
2. conducts a pump-line inspection and confirms safe supports and couplings;
3. completes reinforcement, cover, formwork, falsework, embedded-item, and access inspections;
4. establishes truck sequencing and radio communication;
5. sets up temperature, slump, air, and strength sampling procedures;
6. installs windbreaks and prepares curing materials;
7. divides the slab into planned placing zones and lift directions;
8. assigns trained vibrator operators and finishing crews; and
9. records batch tickets, arrival times, test results, placement locations, and curing actions.

Concrete is placed close to its final position, consolidated systematically around congested reinforcement, and finished only after bleed water has dissipated. Curing begins promptly with an approved method. If supply is interrupted, the supervisor stops placement at the predetermined joint rather than creating an uncontrolled discontinuity.

Outcome

The pour is completed within the extended shift plan without visible segregation or cold joints. Strength results meet the acceptance criteria, and the records allow each truck and test specimen to be traced to a slab zone. The principal success was not a single equipment choice but integration of production, logistics, temporary works, reinforcement, testing, weather protection, and contingency planning.

Learning points

• Theoretical equipment capacity is not practical production capacity.
• A placing plan must address interruption, not only normal operation.
• Congested reinforcement affects mix selection, pumpability, vibration, and inspection.
• Weather planning is part of quality control.
• Traceable records support both acceptance and later investigation.

13. Common Defects and Corrective Thinking

Honeycombing may result from inadequate vibration, congested reinforcement, leaking forms, harsh mixture, or excessive lift thickness. The response is to determine depth and structural significance before repair; cosmetic patching is not adequate for serious voids.

Cold joints arise from delays, poor sequencing, or insufficient consolidation between layers. Prevention includes reliable supply, planned lifts, standby resources, and properly prepared construction joints.

Plastic shrinkage cracking is associated with rapid evaporation before sufficient surface strength develops. Wind reduction, cooling, timely finishing, and immediate curing reduce risk.

Bleeding and settlement cracking can result from excessive water, poor grading, high slump, or inadequate mixture stability. Corrective action begins with mixture and placement review.

Dimensional defects often originate in formwork movement, settlement, inaccurate surveying, or premature stripping. Temporary works inspection and controlled stripping are essential.

Best-Practice Checklist

Before production: approve materials and mixture; calibrate equipment; check moisture corrections; plan logistics; review weather and safety controls.

Before placement: inspect formwork, falsework, reinforcement, embedded items, access, pump lines, lighting, testing equipment, and curing materials.

During placement: control delivery time and consistency; avoid unauthorized water addition; place in planned lifts; consolidate systematically; monitor forms; maintain records.

After placement: protect the surface; begin curing; control loading and stripping; inspect finish; test specimens; document defects and corrective action.

Throughout the work: communicate clearly, stop unsafe operations, preserve traceability, and treat specifications and standards as minimum controls rather than substitutes for professional judgment.

Chapter Summary

Concrete construction is an integrated process in which material proportioning, batching, mixing, transport, pumping, placement, consolidation, finishing, curing, formwork, reinforcement, and testing jointly determine performance. Mass batching, moisture correction, controlled water–cementitious-material ratio, uniform mixing, and reliable delivery establish the production foundation. Pumping and placement must prevent segregation and cold joints, while systematic vibration ensures contact with forms and reinforcement. Finishing must follow suitable surface conditions, and curing must protect hydration from moisture loss and temperature extremes.

Formwork and falsework require a complete load path, adequate stiffness, stability, inspection, and controlled stripping. Reinforcement must satisfy location, cover, anchorage, and constructability requirements. Precast and prestressed methods offer speed and quality benefits but demand careful handling, connection design, stressing control, and safety exclusion zones. Fresh and hardened tests provide evidence of conformity, but results must be interpreted through sampling procedures, variability, and governing acceptance criteria. Effective quality control combines inspection, testing, records, competent personnel, safety management, sustainability, and contingency planning.

Key Terms

Batching: Measuring concrete ingredients for a defined batch.

Water–cement ratio: Mass of water divided by mass of cement.

Water–cementitious-material ratio: Mass of water divided by total cementitious-material mass.

Admixture: A material added to concrete other than cement, water, and aggregate to modify properties.

Segregation: Separation of concrete constituents during handling or placement.

Bleeding: Upward movement of water in fresh concrete.

Consolidation: Removal of entrapped air and improvement of concrete contact and density.

Curing: Maintaining moisture and temperature conditions for hydration and strength development.

Formwork: Temporary or permanent mould used to shape and support concrete.

Falsework: Temporary support system for formwork, concrete, or construction loads.

Concrete cover: Distance from the concrete surface to the specified reinforcement surface.

Precast concrete: Concrete manufactured away from its final structural location.

Prestressing: Introducing intentional force to improve structural performance.

Pre-tensioning: Stressing tendons before concrete is cast.

Post-tensioning: Stressing tendons after concrete has hardened.

Slump: A standardized indication of fresh-concrete consistency.

Yield: Actual concrete volume relative to theoretical batch volume.

Quality assurance: Planned system providing confidence that requirements will be met.

Quality control: Operational inspection and testing used to verify conformity.

Cold joint: A discontinuity formed when successive concrete layers do not properly unite.

Review Questions

Short Answer Questions

1. Why is mass batching generally more reliable than volume batching for concrete production?
2. Define segregation and state two methods of preventing it.
3. What are the principal functions of concrete curing?
4. Distinguish formwork from falsework.
5. Why must reinforcement be inspected before forms are closed?

Long Answer Questions

1. Explain the complete sequence from batching through curing and identify the main quality risks at each stage.
2. Discuss the design and inspection requirements for formwork and falsework.
3. Compare site-cast, precast, pre-tensioned, and post-tensioned concrete construction.
4. Explain how fresh- and hardened-concrete tests support quality assurance, including their limitations.
5. Develop a quality-control plan for a large reinforced-concrete pour.

Analytical / Application Questions

1. A project requires 300 m³ of concrete. A plant produces 2.5 m³ per batch with a six-minute theoretical cycle. Calculate the theoretical production rate and explain why the scheduled practical rate should be lower.
2. A concrete batch contains 175 kg of water, 350 kg of cement, and 50 kg of supplementary cementitious material. Calculate w/c and w/cm, and explain which ratio governs if the specification uses total cementitious material.
3. During a slab pour, slump is within range but concrete begins segregating at the pump discharge. Diagnose possible causes and propose an immediate response and a longer-term preventive action.

Multiple Choice Questions with Answers

Question 1

Which practice most directly controls the water–cement ratio during batching?

A. Adding water at the point of placement until the desired slump is reached

B. Measuring water and cement by mass using calibrated equipment

C. Increasing vibration time after placement

D. Reducing the duration of curing

Correct Answer: B. Measuring water and cement by mass using calibrated equipment

Question 2

A batch contains 160 kg of water and 320 kg of cement. What is the water–cement ratio?

A. 0.25

B. 0.40

C. 0.50

D. 2.00

Correct Answer: C. 0.50

Question 3

The primary purpose of internal vibration is to:

A. Increase the cement content

B. Remove entrapped air and improve concrete contact

C. Transport concrete horizontally through the form

D. Replace curing

Correct Answer: B. Remove entrapped air and improve concrete contact

Question 4

Which condition most increases the risk of plastic-shrinkage cracking?

A. Low evaporation and protected placement

B. Rapid evaporation from a hot, dry, windy surface

C. Adequate curing immediately after finishing

D. Low concrete temperature with high humidity

Correct Answer: B. Rapid evaporation from a hot, dry, windy surface

Question 5

Falsework is best described as:

A. Permanent reinforcement embedded in concrete

B. A temporary support system for formwork and construction loads

C. A chemical admixture used to reduce water

D. A test method for compressive strength

Correct Answer: B. A temporary support system for formwork and construction loads

Question 6

Which item is most important before closing reinforced-concrete forms?

A. Confirming reinforcement size, spacing, location, and cover

B. Removing all reinforcement supports

C. Adding unapproved water to the concrete

D. Starting power trowelling

Correct Answer: A. Confirming reinforcement size, spacing, location, and cover

Question 7

In post-tensioned concrete, tendons are generally stressed:

A. Before aggregate is delivered

B. Before the formwork is erected

C. After the concrete has hardened sufficiently

D. Only after the structure is demolished

Correct Answer: C. After the concrete has hardened sufficiently

Question 8

For a concrete specimen tested in compression, nominal compressive stress is calculated as:

A. Load multiplied by area

B. Area divided by load

C. Load divided by loaded area

D. Mass divided by volume

Correct Answer: C. Load divided by loaded area

Question 9

Which statement about slump is correct?

A. It is a direct measurement of compressive strength

B. It indicates consistency but must be interpreted with mixture and placement information

C. It replaces all strength testing

D. It measures reinforcement cover

Correct Answer: B. It indicates consistency but must be interpreted with mixture and placement information

Question 10

The most appropriate response to an unexpected concrete-delivery interruption during a major pour is to:

A. Continue placing randomly until concrete arrives

B. Add uncontrolled water to the previous layer

C. Use the predetermined construction-joint and emergency procedure

D. Remove all reinforcement immediately

Correct Answer: C. Use the predetermined construction-joint and emergency procedure