Tentative Guidelines for Construction of Cement Concrete Pavements in Hot Weather

The Introduction of IRC 61 provides a chart (Fig. 1) for calculating the rate of evaporation of surface moisture from concrete based on air temperature, relative humidity, concrete temperature, and wind velocity. The chart is used by entering the air temperature scale and following the dotted line to the rate of evaporation scale. This is critical for understanding curing conditions. Additionally, Table 1 lists key contributors to the code development. No explicit formulas are given in the introduction, but the evaporation rate chart serves as a practical tool for field assessment.

Sources: Fig. 1, Table 1

Hot weather concreting in IRC 61 highlights problems like rapid water evaporation, increased slump loss, early stiffening, and reduced strength. Key remedial measures include:

• Use of chilled mixing water or ice to reduce concrete temperature.
• Use of retarders to delay setting time.
• Scheduling concrete placement during cooler parts of the day.
• Providing adequate curing immediately after placement to prevent moisture loss.
• Using fog sprays or wet coverings to maintain surface moisture.

Though specific formulas or tables are not provided in the retrieved context, these guidelines are essential to mitigate hot weather effects on cement concrete pavements as per IRC 61 sections 3 and 4.

Summary:

• Problems: rapid evaporation, slump loss, early setting, strength reduction.
• Remedies: chilled water, retarders, timing, curing, moisture maintenance.

This ensures durability and performance of concrete pavements in hot climates.

Sources: Clause 3, Clause 4

Hot weather accelerates cement hydration, reducing setting time and increasing water demand, which can lower strength and increase plastic shrinkage. To mitigate this, avoid rapid hardening cement and use set-retarding and water-reducing admixtures like sugar (0.05% by weight of cement) to delay setting by about 2 hours at 44°C, improving workability and strength (Clause 4.2.5, 4.5.1, 4.5.2).

Aggregate temperature greatly affects concrete temperature; cooling aggregates by shading or sprinkling water reduces concrete temperature effectively (Clause 4.4, 5.1). Ice can be used as part of mixing water to lower temperature due to latent heat of fusion (79.6 cal/gm) but must fully melt to avoid voids (Clause 4.2.5).

For temperature control, reducing cement temperature by 4°C, water by 2°C, or aggregate by 1°C lowers concrete temperature by 0.5°C (Clause 5.1).

Operational measures include minimizing batching/mixing time, painting mixers white, ensuring equipment readiness, and planning joints to avoid delays (Clause 5.2, 5.3).

Sources: Clause 4.2.5, Clause 4.4, Clause 4.5.1, Clause 4.5.2, Clause 5.1, Clause 5.2, Clause 5.3

Key remedial measures against adverse effects of hot weather concreting per IRC 61 include:

• Use of Ice in Mixing Water: Ice (latent heat 79.6 cal/gm) can be added to mixing water to reduce concrete temperature; ensure complete melting to avoid voids. Account ice quantity in total water (Clause 4.2.5).

• Avoid Rapid Hardening Cement: Hot weather accelerates cement hydration and setting, increasing water demand and plastic shrinkage; rapid hardening cement should be avoided (Clause 4.2.5).

• Aggregate Temperature Control: Aggregates should be stored under shade and kept cool by sprinkling or inundation to reduce concrete temperature, as aggregates have the largest effect on concrete temperature (Clause 4.4, 5.1).

• Use of Set-Retarding and Water-Reducing Admixtures: Calcium ligno-sulphonate, carbohydrates (notably sugar at 0.05%), and certain metal sulphates retard setting and reduce water demand. Sugar addition can delay setting by ~2 hours at 44°C and improve workability and strength, but dosage must be controlled (Clauses 4.5.1, 4.5.2).

• Batching and Mixing Practices: Minimize batching and mixing times, paint mixer white to reduce heat absorption, maintain mixer and equipment efficiency, and locate batching units close to placement site (Clause 5.2).

• Formwork and Placement: Cover formwork externally with wet earth, place concrete promptly to avoid rehandling, ensure availability and maintenance of vibrators and manpower, and plan joints and materials in advance to avoid delays (Clause 5.3).

• Temperature Reduction Ratios: To reduce concrete temperature by 0.5°C, reduce cement temperature by 4°C, water by 2°C, or aggregate by 1°C; aggregate temperature control is most effective (Clause 5.1).

These guidelines help mitigate rapid setting, strength loss, and plastic shrinkage due to hot weather.

Sources: Clause 4.2.5, Clause 4.4, Clause 4.5.1, Clause 4.5.2, Clause 5.1, Clause 5.2, Clause 5.3

Key specifications for production, placement, and curing of concrete per IRC 61 include:

• Temperature Control: The temperature of freshly mixed concrete can be estimated from the temperatures and weights of aggregates, cement, and water using the formula:

  [ I = \frac{0.22(W_a t_a + W_e t_e) + W_w t_w}{0.22(W_a + W_e) + W_w} ]

  where weights (W) are in kg, temperatures (t) in °C, and 0.22 is the specific heat for aggregates and cement (Clause 5.1).

• Use of Ice: Ice can be added to mixing water to reduce temperature, accounting for latent heat of fusion (79.6 cal/gm) (Clause 4.2.5).

• Batching and Mixing: Minimize batching and mixing times; paint mixer white to reduce heat absorption; maintain equipment to avoid delays (Clause 5.2).

• Placement: Place concrete as close to final position as possible to avoid rehandling; ensure sufficient vibrators and manpower; plan joints and materials in advance (Clause 5.3).

• Curing: Start initial curing early using wet hessian cloth; continue curing by ponding for a minimum of 28 days; membrane curing with plastic sheets is not permitted; liquid membranes like sodium silicate may be used if water is scarce but may reduce strength slightly (Clause 11.00).

• Quality Control: Conduct tests promptly on samples; monitor air and concrete temperature, wind velocity, humidity, and weather conditions; record all observations during work (Clause 5.7).

Sources: Clause 5.1, Clause 4.2.5, Clause 5.2, Clause 5.3, Clause 11.00, Clause 5.7

The temperature of freshly mixed concrete can be estimated from the temperatures and proportions of the mix ingredients using the following formulas from IRC 61:

Case I: Without addition of ice [ T = \frac{W_a t_a S_o + W_c t_c S_c + W_w t_w S_u}{W_a S_a + W_c S_c + W_w S_u} ] where:

• (T) = temperature of freshly mixed concrete (°C)
• (W_a, W_c, W_w) = weights of aggregate, cement, and water (kg)
• (t_a, t_c, t_w) = temperatures of aggregate, cement, and water (°C)
• (S_a = S_c = 0.22), (S_u = 1) (specific heats in cal/gm°C)

This reduces to:

[ T = \frac{0.22 (W_a t_a) + W_c t_c + W_w t_w}{0.22 (W_a + W_c) + W_w} ]

Case II: With addition of ice

The formula modifies to include ice weight (W_i) and latent heat:

[ T = \frac{0.22 (W_a t_a) + W_c t_c + (W_w - W_i) t_w + W_i \times (-79.6)}{0.22 (W_a + W_c) + W_w} ]

where (-79.6) cal/gm is the latent heat of fusion of ice.

Note: If aggregates contain free water, its temperature is considered same as aggregate, and water added at mixer is adjusted accordingly.

These formulas are per the IRC 61 clauses on estimation of concrete temperature from mix ingredients and their temperatures.

Sources: Clause on Estimation of Temperature of Freshly Mixed Concrete

In hot weather concreting as per IRC 61, key specifications for admixtures include:

• Use set-retarding and water-reducing admixtures to offset accelerated setting and increased water demand (Clause 4.5.1).
• Common set-retarders: calcium ligno-sulphonate, carbohydrates (notably sugar), calcium salts, and sulphates of zinc, aluminium, copper, iron (Clause 4.5.2).
• Dosage: typically 0.05 to 0.5% by weight of cement. For sugar, 0.05% addition can retard setting by about 2 hours at 44°C and improve workability and strength, enabling up to 4% cement saving (Clause 4.5.2).
• Admixtures should be added to mixing water.
• Avoid overdosing as it may cause harmful effects.

Additional measures include cooling aggregates (stack under shade, sprinkle water), using ice as part of mixing water to reduce temperature, and controlling batching/mixing times to minimize temperature rise (Clauses 4.2.5, 4.4, 5.1, 5.2).

These guidelines help maintain concrete quality and workability in hot weather conditions.

Sources: Clause 4.5.1, Clause 4.5.2, Clause 4.2.5, Clause 4.4, Clause 5.1, Clause 5.2

Control of mixing water and aggregate temperatures in hot weather concreting is critical to maintain workability and strength. As per IRC 61 Clause 4.2.2, increasing concrete temperature by 11°C can reduce slump by about 2.5 cm, requiring 3-4% more water at 30°C to 50°C, which increases w/c ratio and reduces strength. Clause 4.2.4 highlights that water temperature significantly affects concrete temperature due to its high specific heat; thus, chilled water and insulated, white-painted water tanks and pipes are recommended to keep water cool. Aggregate temperature also influences concrete temperature and moisture loss; aggregates should be stored in shade and kept cool by sprinkling water (Clause 4.4).

The temperature of freshly mixed concrete can be estimated by the formula (Clause 4.2.2):

[ T_c = \frac{0.22(W_a T_a + W_c T_c) + W_w T_w}{0.22(W_a + W_c) + W_w} ]

where weights (W) and temperatures (T) of aggregate (a), cement (c), and water (w) are used, with specific heat of aggregate and cement as 0.22 and water as 1. Ice addition modifies this formula by including latent heat of fusion (79.6 cal/gm) (Clause 4.2.5).

Additional measures include using set-retarding and water-reducing admixtures to offset accelerated setting and water demand (Clause 4.5), minimizing batching and mixing times, and maintaining equipment efficiency (Clause 5.2). Formwork should be kept wet to reduce heat gain (Clause 5.3).

Sources: Clause 4.2.2, Clause 4.2.4, Clause 4.4, Clause 4.2.5, Clause 4.5, Clause 5.2, Clause 5.3

Key guidelines for batching, mixing, and transportation of cement concrete in hot weather per IRC 61 include:

• Temperature Control of Ingredients: The temperature of freshly mixed concrete (I) can be estimated from the temperatures and weights of aggregates (Wa), cement (Wo), and water (Ww) using the formula:

  I = [0.22(Wa * ta + Wo * te) + Ww * tw] / [0.22(Wa + Wo) + Ww]

  where ta, te, tw are temperatures of aggregate, cement, and water respectively, and 0.22 is the specific heat for aggregate and cement (Clause 4.2.5).

• Use of Ice: Partial replacement of mixing water with ice reduces concrete temperature further, accounting for latent heat of fusion (79.6 cal/gm) (Clause 4.2.5).

• Batching and Mixing: Minimize batching and mixing times for uniformity. Paint mixer white externally to reduce heat absorption. Check mixer blades frequently to avoid efficiency loss (Clause 5.2).

• Transportation: Use sufficient wheelbarrows or taslas to minimize transport time. Locate batching/mixing units close to placement to reduce lead time (Clause 5.2).

• Equipment and Work Planning: Maintain adequate vibrators and manpower to avoid delays. Plan joints and materials in advance to prevent placement delays (Clause 5.3).

• Curing: Start curing early with wet hessian cloth and continue for at least 28 days. Membrane curing is not permitted except liquid membranes where water is scarce (Clause 11.00).

These measures help control temperature rise, prevent rapid setting, and ensure quality concrete in hot weather conditions.

Sources: Clause 4.2.5, Clause 5.2, Clause 5.3, Clause 11.00

Key specifications for placing, compacting, and finishing concrete per IRC 61 include:

• Placing Speed & Coordination: Concrete should not be placed faster than it can be properly compacted and finished with available equipment and manpower (Clause 5.5).

• Layer Thickness: Follow thickness stipulations for individual layers in two-layer construction as per IRC:15-1970 (Clause 5.5).

• Covering Fresh Concrete: Use tarpaulins on travelling stands to cover concrete during noon to protect from heat (Clause 5.6). A typical cover stand includes M.S. angles, tubing, plates, and wheels with a span of 4.5 m (Fig. 2).

• Compacting Equipment: Ensure sufficient screed and needle vibrators with standby units and adequate manpower; maintain equipment in good order to avoid delays (Clause 5.3).

• Placing: Place concrete as close as possible to final position to avoid rehandling (Clause 5.3).

• Environmental Control: In hot weather, cover concrete with wet gunny bags or hessian cloth early to reduce thermal stresses; consider evening or night concreting (Clause 5.4).

These guidelines ensure quality and durability during placing, compacting, and finishing operations under varying conditions.

Sources: Clause 5.4, Clause 5.5, Clause 5.6, Clause 5.3

As per IRC 61 Clause 11.00, curing of concrete in hot weather requires starting initial curing early using wet hessian cloth, followed by thorough ponding for a minimum of 28 days. Membrane curing with plastic sheets is not permitted; however, liquid membranes like sodium silicate or silicones may be used if water is scarce, though they may slightly reduce strength. Protective measures include covering freshly laid concrete with tarpaulins mounted on cover stands (typical cover stand details are given in Fig. 2) to shield from heat during peak hours (11 a.m. to 5 p.m.).

Key specifications:

• Minimum curing period: 28 days (Clause 11.00)
• Use of wet hessian cloth for initial curing
• Ponding must be thorough with regular water supply
• Plastic membrane curing is prohibited
• Liquid membrane curing allowed only if water is scarce
• Cover stands for sheltering concrete: span 4-5 m, clearance 0.25-0.30 m, made of M.S. angles, tubing, and plates as per Fig. 2

Additional protective measures include:

• Covering formwork with wet earth
• Speeding up placing, compacting, and finishing operations
• Using tarpaulins on travelling stands during noon hours

These measures help control temperature, prevent rapid moisture loss, and ensure quality curing in hot weather conditions.

Sources: Clause 11.00, Fig. 2

Key quality control and testing procedures for cement concrete pavements in hot weather per IRC 61 include:

• Conduct quality control tests as per IRC: SPL. 11-1973 promptly on concrete samples to reflect actual conditions, with special care for specimen protection and curing (Clause 5.7).
• Monitor and record environmental parameters: air temperature, concrete temperature, wind velocity, relative humidity, and weather conditions (Clause 5.7).
• Maintain detailed records of concrete appearance, timing of stages, curing start time, and protective measures during construction (Clause 5.7).
• Ensure curing period is not less than 28 days; initial curing with wet hessian cloth starting early, followed by thorough ponding; membrane curing with plastic membranes is not permitted (Clause 11.00).

For estimating freshly mixed concrete temperature without ice, use:

I = [0.22(Wa ta + Wd td) + Wo to] / [0.22(Wa + Wd) + Wo]

Where Wa, Wd, Wo are weights of aggregates and cement; ta, td, to are their temperatures; 0.22 is specific heat for aggregates and cement (Clause None).

With ice addition, the formula adjusts to account for ice weight and latent heat (Clause None).

Sources: Clause 5.7, Clause 11.00, Clause None (Temperature estimation)

For hot weather concreting planning and scheduling per IRC 61, key points include:

• Temperature Control at Mixing: Reducing concrete temperature by 0.5°C requires lowering cement temperature by 4°C, water by 2°C, or aggregate by 1°C. Aggregates should be kept cool by shading or sprinkling water (Clause 5.1).

• Use of Ice: Ice can replace part of mixing water to reduce temperature; latent heat of ice (79.6 cal/gm) aids cooling. Ice must fully melt during mixing to avoid voids (Clause 79.6).

• Admixtures: Set-retarding and water-reducing admixtures (e.g., sugar at 0.05%) can offset accelerated setting and reduce water demand (Clause 4.5).

• Mixing Time & Equipment: Minimize batching/mixing time, maintain equipment, and ensure sufficient transport means to avoid delays (Clause 5.2).

• Curing: Start early curing with wet hessian cloth, continue ponding for at least 28 days; membrane curing generally not permitted (Clause 5.6).

• Temperature Estimation Formula: Without ice,

  [ T_c = \frac{0.22(W_a T_a + W_{ad} T_{ad}) + W_c T_c}{0.22(W_a + W_{ad}) + W_c} ]

  With ice addition, formula accounts for ice latent heat (79.6 cal/gm) and weights (Clause 5.1 Appendix).

These guidelines ensure quality and durability in hot weather concreting by controlling temperature, setting time, and curing.

Sources: Clause 79.6, Clause 4.4, Clause 4.5, Clause 5.1, Clause 5.2, Clause 5.6

IRC 61 includes illustrative examples and appendices that provide key formulas and guidelines for cement concrete pavements, especially under hot weather conditions. One important formula is for the calculation of the rate of evaporation of surface moisture from concrete, which depends on air temperature, humidity, concrete temperature, and wind velocity, as shown in Figure I. Additionally, tentative guidelines for construction in hot weather are provided to ensure quality and durability. The document also contains a table listing contributors and experts involved in its preparation, reflecting the collaborative nature of the code development.

Sources: Illustrative Example: Rate of evaporation formula in Fig. I, Table 1: Introduction with contributors