Admixtures, Curing and Thermal Control

Introduction and Context

Concrete performance is governed not only by cement, water and aggregate selection, but also by the control of chemical reactions and moisture–temperature history after mixing. Admixtures modify fresh and hardened concrete properties; curing preserves the moisture and temperature conditions required for hydration; and thermal control limits temperature differentials and restraint stresses that can produce early-age cracking. These three subjects are therefore interdependent.

A technically appropriate solution depends on exposure, structural function, construction sequence, ambient conditions, concrete volume and required performance. A high-range water reducer may reduce water content and permeability, but may also cause rapid slump loss when incompatible with a cement–supplementary cementitious material system. Extended moist curing can improve strength and durability, but may be difficult on vertical surfaces or in cold weather. In mass concrete, reducing peak temperature is insufficient if the temperature difference between the interior and surface becomes excessive.

This chapter develops a selection and control framework for normal, hot-weather, cold-weather and mass-concrete construction, with particular attention to admixture compatibility and early-age cracking.

Learning Objectives

After studying this chapter, the reader should be able to:

1. Explain the mechanisms and applications of major concrete admixtures.

2. Select admixture systems for normal, hot-weather, cold-weather and mass-concrete placement.

3. Design and verify curing regimes using strength, durability and temperature criteria.

4. Analyse thermal development, restraint and early-age cracking risk.

5. Diagnose admixture incompatibility and propose trial-mix and field-control procedures.

6. Integrate technical, contractual, environmental and quality-management considerations in concrete production.

1. Admixtures as Performance-Design Tools

An admixture is a material other than water, aggregate, hydraulic cement or fibre that is added to concrete before or during mixing to modify one or more properties. Admixtures should not be regarded as substitutes for sound mixture proportioning, adequate consolidation or proper curing. Their function is to provide controlled modification within a verified concrete system.

1.1 Main categories

Water-reducing admixtures disperse cement particles and reduce the water required for a specified workability. Conventional water reducers generally provide moderate water reduction, while high-range water reducers (HRWRs), commonly called superplasticizers, provide substantially greater fluidity or permit lower water-to-binder ratio. Polycarboxylate ether systems are widely used in modern high-performance concrete because their steric dispersion can provide high water reduction, although they may be sensitive to cement chemistry and may produce rapid slump loss or excessive air entrainment.

Set accelerators shorten setting time and increase early strength. They are useful in cold weather, repair work and rapid construction. Calcium chloride can accelerate hydration effectively in plain concrete, but its use is restricted or prohibited in prestressed concrete and in reinforced concrete where corrosion risk is significant. Non-chloride accelerators are preferred where reinforcement, embedded metals or durability requirements make chloride addition unacceptable.

Retarding admixtures delay setting and are useful in hot weather, long transport times, large pours and complex placements. Excessive dosage can cause severe retardation, bleeding, strength delay or surface defects. Retarders do not eliminate the need for temperature reduction and evaporation control.

Air-entraining admixtures introduce a stable system of microscopic, closely spaced air voids. These voids improve resistance to freezing and thawing by providing pressure-relief spaces for water that freezes within the paste. Entrained air is not equivalent to accidental entrapped air: entrained voids are smaller and more uniformly distributed. Air content must be controlled because excessive air reduces strength, while air loss during pumping or finishing can reduce durability.

Viscosity-modifying admixtures (VMAs) increase cohesion and reduce segregation and bleeding. They are especially useful in self-consolidating concrete, underwater concrete and mixtures containing difficult aggregate gradations. VMA dosage must be coordinated with HRWR dosage because excessive viscosity can impair filling, pumping and surface finishing.

Shrinkage-reducing admixtures reduce capillary surface tension and can lower drying-shrinkage strain. They may affect setting, strength development and air entrainment, and are normally evaluated with the complete mixture rather than in isolation.

Corrosion-inhibiting admixtures reduce reinforcement corrosion risk through mechanisms such as anodic inhibition or modification of the pore solution. They are not a replacement for adequate cover, low permeability, crack control and appropriate detailing.

Waterproofing and permeability-reducing systems include hydrophobic materials, pore-blocking agents and crystalline admixtures. Their effectiveness depends strongly on crack control and curing; no admixture can make a poorly compacted or extensively cracked concrete watertight.

Expansive and compensating-shrinkage admixtures generate controlled expansion, commonly through formation of ettringite or calcium hydroxide, to offset restrained drying shrinkage. They require carefully controlled water, curing and restraint conditions. Uncontrolled expansion can damage concrete.

1.2 Mechanisms affecting fresh concrete

Cement particles flocculate in water because of electrostatic attraction and particle interactions. Flocculation traps mixing water within clusters. Dispersing admixtures separate these particles, releasing water and increasing flow. The practical result may be either:

• increased slump at constant water content; or
• reduced water content at constant slump.

The second approach is usually more beneficial because it can reduce the water-to-binder ratio, porosity and permeability. However, flowability depends on paste volume, aggregate grading, temperature, mixing energy, elapsed time and chemical compatibility. A dosage that performs well in a laboratory mixer may not perform identically in a ready-mix truck or batching plant.

Set control is affected by cement mineralogy, sulfate balance, alkali concentration, supplementary cementitious materials, temperature and admixture sequence. Therefore, dosage should be expressed as a trial-tested range rather than treated as a universal fixed value.

1.3 Selection principles

Admixture selection should follow a performance specification:

1. Define required slump or slump flow, setting window, strength, durability, air content and placing method.

2. Identify environmental conditions and construction constraints.

3. Select candidate admixtures from technically compatible product families.

4. Conduct laboratory and field trials using the actual cement, supplementary materials, aggregates, water and mixing equipment.

5. Measure initial and retained workability, setting, air content, bleeding, temperature, strength and relevant durability indicators.

6. Establish dosage tolerances, storage requirements, dispensing accuracy and acceptance criteria.

Compatibility is a system property, not simply a property of two products. A cement may be compatible with an HRWR at one temperature and incompatible at another. The use of several products can create synergistic or antagonistic effects. Typical symptoms of incompatibility include flash set, excessive retardation, rapid slump loss, abnormal air-void structure, bleeding, segregation and unstable dosage response.

A practical compatibility assessment records slump or slump flow immediately after mixing and at specified intervals, such as 30, 60 and 90 minutes. It should also record setting time, air content, temperature and early strength. If air entrainment is required, hardened air-void analysis is more reliable than fresh-air measurement alone because pumping and finishing can change the void system.

2. Curing: Preserving the Conditions for Hydration

Curing is the maintenance of adequate moisture and temperature in concrete for a defined period after placement. Hydration consumes water and generates heat. If the surface dries before the pore structure develops, hydration stops locally, permeability increases and plastic or drying shrinkage cracking becomes more likely.

2.1 Objectives of curing

Curing aims to:

• maintain moisture for cement hydration;
• maintain a suitable temperature for strength development;
• reduce permeability and improve durability;
• improve abrasion and freeze–thaw resistance;
• limit plastic shrinkage and surface dusting;
• reduce thermal and moisture gradients;
• develop the specified strength before loading or exposure.

Curing begins immediately after finishing or, where finishing is unnecessary, as soon as the surface will not be damaged by the selected method. The critical early period may last hours or days, but the required duration depends on cement type, temperature, mixture composition, exposure and performance requirements.

2.2 Curing methods

Water curing includes ponding, immersion, spraying and wet coverings. It is highly effective where practical, but continuous water supply and protection from thermal shock are necessary. Applying cold water to a hot concrete surface can create damaging temperature gradients.

Moist coverings such as wet burlap or curing mats are effective if they remain continuously wet and are protected from wind. Intermittent wetting can cause repeated wetting and drying, which may be less effective than continuous protection.

Membrane-forming curing compounds reduce moisture loss by forming a film. They are useful for slabs and large surfaces where water curing is impractical. The compound must be applied at the specified coverage rate and compatible with subsequent coatings, overlays or joint sealants.

Sheet curing uses plastic or waterproof paper. Sheets must be sealed at laps and edges; otherwise local drying occurs. Dark sheets can increase solar heating, whereas reflective sheets reduce heat gain.

Internal curing supplies water from saturated lightweight aggregate, superabsorbent polymers or other reservoirs within the concrete. It can reduce autogenous shrinkage, especially in low-water-to-binder-ratio concrete, but requires mixture-specific proportioning and verification.

2.3 Curing and strength development

For a simplified maturity treatment, the Nurse–Saul maturity index is commonly written as

\[

M=\sum (T_a-T_0)\Delta t

\]

where \(M\) is the maturity index, \(T_a\) is the average concrete temperature during interval \(\Delta t\), \(T_0\) is the datum temperature below which hydration is assumed negligible, and time and temperature must use consistent units. This relationship assumes that concrete strength is primarily related to its temperature history and that the mixture remains otherwise comparable. It is an approximation and should be calibrated with specimens cured at known temperatures. It is not reliable when the concrete experiences significant moisture loss, unusual temperature histories or changing mixture composition.

The Arrhenius-based equivalent-age method is often more theoretically appropriate because hydration rate depends nonlinearly on absolute temperature. It requires an activation energy or rate constant determined for the particular cementitious system. Maturity methods support in-place strength estimation, but they do not by themselves demonstrate durability or adequate curing quality.

3. Thermal Behaviour and Early-Age Cracking

Hydration is exothermic. Heat is generated internally and dissipated through the formwork, exposed surfaces and surrounding ground. In thin members, heat loss is relatively rapid. In mass concrete, the interior may retain heat while the surface cools, producing large temperature differences.

Thermal cracking occurs when restrained thermal contraction produces tensile stress greater than the developing tensile strength or fracture resistance of the concrete. A simplified conceptual relationship is

\[

\sigma_t \approx R E_c \alpha_c \Delta T

\]

where \(\sigma_t\) is induced tensile stress, \(R\) is the degree of restraint between zero and one, \(E_c\) is the relevant early-age elastic modulus, \(\alpha_c\) is the coefficient of thermal expansion, and \(\Delta T\) is the effective temperature change. This is a screening relationship, not a complete cracking model. Creep and relaxation reduce stress, while restraint geometry, temperature gradients, construction joints and evolving material properties must be considered in detailed analysis.

Cracking risk can be expressed conceptually through a thermal cracking index:

\[

I_{cr}=\frac{f_t}{\sigma_t}

\]

where \(f_t\) is the tensile strength at the relevant age. Values below unity indicate that calculated tensile stress exceeds tensile strength in the simplified assessment. Fracture energy, crack-band behaviour, creep, stochastic defects and actual restraint should be included in advanced finite-element analysis.

Early-age cracking has several mechanisms:

• Plastic shrinkage cracking: evaporation exceeds bleeding and the surface contracts while concrete is still plastic.
• Plastic settlement cracking: solid particles settle and movement is interrupted by reinforcement or geometry.
• Autogenous shrinkage: self-desiccation causes volume reduction in low-water-to-binder-ratio systems.
• Thermal contraction cracking: cooling occurs while the member is restrained.
• Drying shrinkage cracking: moisture loss after hardening causes restrained contraction.
• Temperature-gradient cracking: the surface and core experience different temperatures and strains.

3.1 Control measures

Control should begin at mixture design and continue through construction:

• reduce cementitious heat through optimized binder content and suitable supplementary materials;
• use low-heat or moderate-heat cement where appropriate;
• reduce placing temperature by shading aggregates, using chilled mixing water or, where justified, flake ice;
• limit lift thickness and sequence placements to control heat accumulation;
• insulate surfaces to reduce rapid cooling;
• use embedded cooling pipes for very large placements when analysis demonstrates their need;
• provide adequate reinforcement and contraction joints;
• reduce restraint through appropriate geometry and construction sequencing;
• control evaporation using windbreaks, fogging, evaporation-retarding agents and immediate curing;
• monitor temperature at the core, near the surface and at the ambient boundary.

Evaporation-retarding agents are temporary surface treatments and should not be confused with curing compounds. They reduce surface moisture loss during finishing but do not provide a complete curing regime.

4. Environmental and Structural Applications

4.1 Normal-weather concrete

In moderate conditions, the preferred system is usually a water reducer or HRWR selected to achieve required workability without excess water, together with an appropriate curing method. The main risks are uncontrolled slump adjustment with site-added water, inadequate curing and variability in air content. Concrete should be placed, compacted and finished within the verified setting window.

4.2 Hot-weather concrete

Hot weather increases evaporation, accelerates setting, increases water demand and may reduce slump retention. It can also increase the risk of plastic shrinkage and thermal gradients. A suitable strategy may combine a water reducer with a compatible retarder or slump-retention admixture, cooled materials, shaded aggregate stockpiles, night placement, reduced transport time and immediate curing.

The evaporation rate should be assessed using current weather conditions rather than air temperature alone. Wind speed, relative humidity, concrete temperature and surface temperature all matter. If evaporation is high, placing should be postponed or additional protection introduced. Adding water at the site may restore slump but usually increases the water-to-binder ratio and compromises performance.

4.3 Cold-weather concrete

Low temperatures slow hydration and setting and can delay strength development. Concrete must be protected from freezing until it has developed adequate resistance. The protection system may include heated enclosures, insulated forms, heated mixing water, accelerated cement systems or non-chloride accelerators. The objective is not simply to produce a high temperature: excessive temperature can increase thermal gradients and later shrinkage.

Temperature records and maturity monitoring can support decisions on formwork removal and loading. However, maturity estimates must be calibrated and the concrete must not be allowed to freeze during the vulnerable period. Calcium chloride should generally be excluded where reinforcement corrosion, prestressing steel or embedded metals are concerns.

4.4 Mass concrete

Mass concrete is defined by thermal behaviour rather than a universal member dimension. A relatively thick foundation, dam block, raft or pile cap may qualify when heat generation and heat dissipation produce significant temperature differences. The mixture should be designed for low heat and controlled temperature rise, while construction planning should address lift size, joint treatment, cooling and insulation.

A thermal control plan should specify predicted peak temperature, maximum allowable core-to-surface differential, placing temperature, sensor locations, recording frequency, trigger levels and corrective actions. Limits must be established by the designer and governing specification because acceptable values depend on restraint, material properties, member geometry and cracking sensitivity.

5. Worked Application: Preliminary Thermal Screening

Consider a restrained concrete element for which early-age analysis estimates an effective temperature change of 18°C. Assume a restraint factor \(R=0.65\), early-age modulus \(E_c=12\) GPa and thermal expansion coefficient \(\alpha_c=10\times10^{-6}/°C\). Using the simplified screening relationship:

\[

\sigma_t=R E_c\alpha_c\Delta T

\]

Substitution gives

\[

\sigma_t=0.65(12,000\text{ MPa})(10\times10^{-6}/°C)(18°C)

\]

\[

\sigma_t=1.404\text{ MPa}

\]

If the estimated tensile strength at the critical age is 1.8 MPa, the simplified cracking index is

\[

I_{cr}=\frac{1.8}{1.404}=1.28

\]

The result suggests a margin above unity, but it does not establish that cracking will not occur. Creep relaxation, actual restraint, gradients, construction joints and local defects should be investigated. If tensile strength were only 1.2 MPa, the index would be 0.85, indicating a higher risk and supporting measures such as lower placing temperature, insulation, reduced heat generation or improved crack-control reinforcement.

The example demonstrates why temperature alone is not a sufficient acceptance criterion. Stress depends on restraint, stiffness, expansion coefficient, thermal history and tensile strength.

6. Illustrative Case Study: Raft Foundation in Hot Weather

Background

A 2,400 m³ reinforced-concrete raft for a high-rise building was scheduled for continuous placement during summer. The specified concrete required 50 MPa compressive strength at 56 days, a low permeability classification and a 180 mm slump at discharge. The raft thickness varied from 1.8 to 2.6 m, creating a significant thermal-control problem.

Problem

Initial laboratory trials using a high cement content and HRWR achieved the required strength but showed rapid slump loss after 45 minutes. Predicted core temperature exceeded the project limit, and the surface was vulnerable to plastic shrinkage because afternoon evaporation was high.

Analysis and approach

The project team adopted a performance-based mixture-development programme. Cementitious content was optimized rather than maximized, and a portion of the cement was replaced with a slower-reacting supplementary cementitious material. A polycarboxylate HRWR with verified slump-retention performance was selected. A compatible retarding component was evaluated through trials using the actual cement and aggregate sources.

The construction plan included:

• chilled mixing water and shaded aggregate stockpiles;
• night-time placement;
• reduced delivery time and continuous plant–site communication;
• thermal sensors at the core, near the top surface and at selected edges;
• insulated formwork and surface covers;
• fogging and curing immediately after finishing;
• staged placement and carefully planned construction joints;
• trigger levels for temperature and slump-loss response.

Trial batches were tested at anticipated field temperatures. Slump, air content and temperature were measured at discharge and after 60 minutes. Setting time, compressive strength, permeability-related indicators and thermal development were also assessed.

Outcome

The revised system maintained the placing window, reduced peak heat generation and avoided excessive surface-to-core temperature differences. Continuous monitoring identified one delivery sequence in which concrete temperature began to rise because aggregate cooling was inadequate. The contingency response was to suspend placement temporarily and restore the specified material temperature. No significant thermal cracking was recorded during the monitoring period.

Learning points

The case illustrates that admixture selection, mixture design, curing and thermal control must be designed as one system. Laboratory compatibility testing at a single temperature was inadequate; field-temperature trials were necessary. In addition, a lower peak temperature alone would not have guaranteed success without surface insulation and evaporation control.

7. Quality Assurance, Governance and Sustainability

Admixture products should be traceable by manufacturer, batch, expiry date and storage condition. Dosing equipment requires calibration, and admixtures should not be combined in a common container unless the manufacturer confirms compatibility. Site personnel must know whether a product is intended for direct addition, pre-dilution or delayed addition.

Specifications should identify performance requirements rather than relying solely on brand names. Approval should consider relevant standards, safety data, environmental declarations, chloride and alkali contribution, volatile constituents, storage stability and compatibility with reinforcement and coatings. Health and safety controls are required for handling corrosive, reactive or hazardous products.

Sustainability decisions should consider the whole life cycle. An admixture that permits lower binder content, longer service life or reduced repair may provide significant environmental benefit. Conversely, excessive use of a chemically intensive system without performance justification may increase cost and environmental burden. Supplementary cementitious materials can reduce embodied carbon, but their slower early strength and temperature sensitivity must be included in curing and construction planning.

Digital batching records, sensor networks and predictive models can improve control. Artificial intelligence may assist in detecting abnormal slump loss, predicting temperature peaks or optimizing trial mixtures, but its outputs require validated data, engineering review and transparent acceptance criteria. AI should support—not replace—materials testing, professional judgement and contractual responsibility.

8. Common Failure Modes and Best Practice

Common failures include adding unapproved water to restore slump, selecting admixtures from isolated product data, ignoring temperature effects on set, curing too late, removing insulation prematurely, applying curing compounds at inadequate coverage and accepting a fresh-air value without considering hardened air-void structure.

Best practice is to maintain a mixture-specific control plan that links each risk to a measurable response. The plan should define target and limit values for slump, slump retention, air, temperature, setting, strength and curing duration. It should also define who can authorize dosage changes, how nonconforming concrete is quarantined and how corrective actions are documented.

The most reliable approach is staged verification: laboratory screening, pilot batching, preconstruction trials, monitored production and post-placement review. This converts admixture and thermal control from an improvised site activity into an engineered process.

Chapter Summary

Admixtures modify concrete performance, but their effectiveness depends on cement chemistry, aggregate characteristics, temperature, dosage, sequence and mixing energy. Water reducers and HRWRs can improve workability or reduce water content; accelerators and retarders control setting; air entrainers provide freeze–thaw protection; VMAs improve cohesion; and specialized products address shrinkage, corrosion and permeability.

Curing preserves moisture and temperature conditions needed for hydration and durability. Water, membrane, sheet, moist-covering and internal-curing methods each have appropriate applications. Maturity methods can estimate in-place strength when calibrated, but they do not replace durability assessment or proper curing.

Thermal control requires attention to heat generation, heat dissipation, restraint, stiffness, thermal expansion, tensile strength and creep. Hot-weather, cold-weather and mass-concrete applications require integrated planning of mixture design, admixtures, placing temperature, curing and monitoring. Compatibility must be established through trials using actual materials and realistic temperatures. Professional control depends on traceability, calibrated equipment, performance-based specifications and documented corrective action.

Key Terms

Admixture: A material added to concrete to modify fresh or hardened properties.

Air-entraining admixture: An admixture that produces a stable system of microscopic air voids.

Autogenous shrinkage: Internal volume reduction caused primarily by self-desiccation during hydration.

Curing: Maintaining moisture and temperature conditions that promote hydration and performance development.

Datum temperature: Assumed temperature below which hydration is negligible in a maturity calculation.

Early-age cracking: Cracking occurring while concrete properties are developing, commonly due to shrinkage or thermal restraint.

Entrapped air: Relatively large, unintended air voids introduced during mixing and consolidation.

High-range water reducer: An admixture that greatly increases workability or reduces water demand.

Internal curing: Supplying water from materials within concrete to support continued hydration.

Mass concrete: Concrete whose dimensions and heat generation create significant thermal-control concerns.

Maturity: A temperature–time index related empirically to strength development.

Plastic shrinkage: Shrinkage of fresh concrete caused by rapid surface moisture loss.

Retarding admixture: An admixture that delays setting.

Thermal cracking index: A ratio comparing tensile resistance with estimated thermal tensile stress.

Thermal restraint: Opposition to free thermal expansion or contraction.

Viscosity-modifying admixture: An admixture that improves cohesion and reduces segregation.

Water reducer: An admixture that lowers water demand for a specified workability.

Water-to-binder ratio: The mass ratio of water to hydraulic and supplementary cementitious binders.

Review Questions

Short Answer Questions

1. Distinguish between entrained and entrapped air in concrete.

2. State two purposes of curing.

3. Why can adding water at the construction site be harmful?

4. Identify three causes of early-age cracking.

5. What information should be recorded during an admixture compatibility trial?

Long Answer Questions

1. Explain the mechanisms, applications and limitations of water reducers, accelerators, retarders and air-entraining admixtures.

2. Compare water curing, membrane curing, sheet curing and internal curing.

3. Discuss the design of a hot-weather concreting plan.

4. Explain why mass concrete requires both core-temperature and surface-temperature monitoring.

5. Discuss how cementitious materials, admixtures and construction sequencing can be integrated to reduce thermal cracking.

Analytical / Application Questions

1. A concrete mixture shows acceptable slump at discharge but severe slump loss after 45 minutes. Develop a systematic investigation and corrective-action plan.

2. A restrained wall has a predicted thermal tensile stress of 1.6 MPa and an estimated early-age tensile strength of 1.3 MPa. Interpret the cracking risk and recommend at least four control measures.

3. Prepare an admixture, curing and temperature-control strategy for a 2 m thick raft placed during winter, identifying required trials, monitoring points and decision triggers.

Multiple Choice Questions with Answers

Question 1

Which admixture primarily improves freeze–thaw resistance by creating microscopic pressure-relief voids?

A. Air-entraining admixture

B. Retarding admixture

C. Viscosity-modifying admixture

D. Corrosion-inhibiting admixture

Correct Answer: A. Air-entraining admixture

Question 2

The main purpose of a high-range water reducer at constant slump is to:

A. Increase aggregate size

B. Reduce water content

C. Increase setting time in every mixture

D. Eliminate the need for curing

Correct Answer: B. Reduce water content

Question 3

Which condition is most directly associated with plastic shrinkage cracking?

A. Rapid surface moisture loss while concrete is still plastic

B. Long-term carbonation only

C. Low aggregate absorption after hardening

D. Excessive reinforcement cover

Correct Answer: A. Rapid surface moisture loss while concrete is still plastic

Question 4

In the simplified thermal stress relationship, the restraint factor represents:

A. The concrete density

B. The degree to which free thermal movement is prevented

C. The cement fineness

D. The air content

Correct Answer: B. The degree to which free thermal movement is prevented

Question 5

Why are field-temperature compatibility trials important for admixtures?

A. Admixture response can change with temperature

B. Temperature has no effect on setting

C. They eliminate the need for strength testing

D. They determine aggregate mineralogy

Correct Answer: A. Admixture response can change with temperature

Question 6

Which measure is generally appropriate for cold-weather reinforced concrete when corrosion risk is important?

A. Use calcium chloride without restriction

B. Use a verified non-chloride accelerator where needed

C. Allow concrete to freeze immediately

D. Remove all curing protection

Correct Answer: B. Use a verified non-chloride accelerator where needed

Question 7

For the maturity expression M = Σ(Ta − T0)Δt, T0 is the:

A. Maximum concrete temperature

B. Datum temperature

C. Ambient relative humidity

D. Final curing duration

Correct Answer: B. Datum temperature

Question 8

A thermal cracking index below unity in the simplified assessment indicates that:

A. Estimated tensile stress exceeds estimated tensile strength

B. No thermal stress exists

C. Concrete has achieved design strength

D. The concrete must contain entrained air

Correct Answer: A. Estimated tensile stress exceeds estimated tensile strength

Question 9

Which is a principal thermal-control measure for mass concrete?

A. Maximizing cement content without analysis

B. Monitoring core and surface temperatures

C. Removing insulation immediately after placement

D. Adding uncontrolled site water

Correct Answer: B. Monitoring core and surface temperatures

Question 10

A viscosity-modifying admixture is principally used to:

A. Increase cohesion and reduce segregation

B. Guarantee higher compressive strength

C. Replace all curing procedures

D. Prevent every form of shrinkage

Correct Answer: A. Increase cohesion and reduce segregation