Peak hydration temperature in the concrete is one the most crucial parameter for concrete cracking during hardening time. Cracking is common to every concrete. when the hydration heat is excessive, cracks develop to dissipate this high heat energy to the environment.

Peak temperature in the concrete

In every construction work, planning the process and sequence well before is mandatory. This will benefit in the smooth construction and get the most effective use from the materials. When it comes to large constructions, calculating the peak hydration temperature in the concrete and cracking potential well before the work is a great advantage. One of the concrete hydration software for prior analysis is ConcreteWorks by Texas department of transportation.

Predicting peak hydration temperature

ConcreteWorks is a concrete durability design tool that capable of predicting hydration temperature, cracking probability, and the chloride service life of the concrete. The software is useful for engineers, researchers, inspectors, and contractors who already know of concrete as well as the construction practice.

The program is easy to download and install. Follow the link down below to download the program.

ConcreteWorks – Download

A thermal analysis of concrete follows in 10 steps. All the inputs are summarized below.

Member Type

4 types of concrete members different from each other are available to select.

General inputs

Units: Select metric or English units. Stick to the exact unit system you selected till the end

Chloride units: This is useful in calculating chloride service life. For temperature predictions, it does not affect.

Starting time: Planned starting time of concrete

Date: Pouring date. It is important to select the correct date of the pour because weather data is involved in the analysis.

Location: give the project location using the closest city of the relevant state. Location is essential for the program to select the corresponding weather data.

Analysis duration: thermal analysis duration and chloride service life analysis times are available to select. The more time is selected program needs more time to calculate.

Shape inputs

Shape inputs corresponds to mass concrete type

The program offers several unique shapes under different member types you selected. The summary of all the shapes is tabulated below.

Mass concreteBridge DeckPrecast concretePavements
Rectangular columnDeck with precast panelBox beam (type 5B40)Rectangular cross-section
Rectangular footingDeck with a metal pan as a formworkType IV – I beam 
Partially submerged rectangular footingDeck made with removable wooden formworkU 40 Beam 
Rectangular bent capGeneric user-defined bridgeU 54 Beam 
Circular column   
Available member types in the program

Member dimensions

Member dimensions adjustment

Each shape will require the main dimensions to carry out the analysis. There are the minimum and maximum dimensions defined by the program.

  • Columns, footings, and rectangular bent caps the minimum dimension is 3 ft.
  • T shaped bent cap has a minimum seat height of 9 inches and a minimum top width of 15 inches
  • Bridge deck thickness is limited to 14 inches
  • Precast thickness is limited to 8 inches
  • For pavements sub-base 1, 2 thicknesses are limited to 24 inches

Mixture proportions

Insert mix proportions

Input the mix proportions and admixtures using in the mix. Common supplementary cementitious materials are available to select. The window also shows a pie chart of mix proportions by their weights. 

The panel provides a link to mix proportion designing too. Add the properties of available material and target characteristics to design the mix.

Material properties

Material property window

This window collects the material properties using in the mix. Cement type and chemical composition are according to the manufactures datasheet.

Cement typeCementApplication
Type I/IIEither type I or type II (both are acceptable)No or moderate sulfate resistance
Type IPortland cementGeneral-purpose (no special properties required)
Type IIPortland composite cement with addition exceeding 5%Moderate sulfate resistance
Type VComposite cementHigh sulfate resistance
Cement types and relevant applications

Aggregate type and the material type of both coarse and fine aggregates should be inserted in the window. The program allows us to use a coarse aggregate mix contain up to 3 different coarse aggregates and a fine aggregate mix having 2 different types.

Mechanical properties

Maturity calculations

Mechanical properties window s relates to the maturity calculation. Nurse – Saul method and equivalent age method is available to select. Check the box saying check to calculate thermal stress when temperatures are calculated for cracking probability analysis. For the calculation of thermal stresses, an equivalent age method must be used.

Construction inputs

Site inputs

Construction-related inputs such as concrete placing temperature, formwork properties, covering blanket properties, and curing methods are available to select in the window. A little tool is available here to calculate the fresh concrete temperature using the initial temperature of the materials. Use this tool to try out different material temperatures to optimize the placing temperature.

Calculate fresh concrete temperature using the tool

Environmental inputs

Environmental effects on the concrete temperature

Following essential weather, inputs are discussed in the environmental input pane. The program uses data from its library. However, you also can enter any desired data set corresponding to your location.

  • Temperature
  • Wind speed
  • Percentage of cloud cover
  • Relative humidity
  • Yearly temperature

Corrosion modeling inputs

Concrete inputs relate to reinforcement, cover, and cast in place parameters, and chloride exposure conditions are selected here.

Input check

Overall input check

The program will summarize all the input you entered. Any unsure or questionable inputs will be highlighted in red. Green ones are within acceptable limits. Creators of ConcreteWorks have listed the following ranges that are suitable for parameters.

ParameterMost suitable range
Rectangular Column Width or Depth3 ft ~ 30 ft
Rectangular Footing Width, Length3 ft ~ 80 ft
Rectangular Footing Depth3 ft ~ 30 ft
Rectangular Bent Cap Width or Depth3 ft ~ 30 ft
T-Shaped Bent Cap Width3 ft ~ 15 ft
T-Shaped Bent Cap Height3 ft ~ 15 ft
Circular Column Diameter3 ft ~ 15 ft
Cement Content100 # ~ 1200 #
Water Content100 # ~ 1200 #
Coarse Aggregate Content100 # ~ 4000 #
Fine Aggregate Content100 # ~ 4000 #
Air Content0% ~10%
Class C Fly Ash Content0 # ~ 1200 #
Class C Fly Ash CaO20 % ~ 30 %
Class F Fly Ash Content0 # ~ 1200 #
Class F Fly Ash CaO0 % ~ 20 %
Slag Content0 # ~ 1200 #
Silica Fume Content0 # ~ 1200 #
Ultra-Fine Fly Ash0 # ~ 1200 #
Any Bogue Compound Content0 % ~ 100 %
Any Bogue Compound that does not
meet ASTM C 150
 
C3A1%
Blaine Fineness280 kg/m3 ~ 1000 kg/m3
Alkali Content0% ~ 100%
Fresh Concrete Placement
Temperature
32 °F ~ 212 °F
PCC age at form removal0 hrs
The delay between removing forms and
cure method application
0
Hydration Parameter alpha0 ~ 1
Suitable ranges for parameters

Results

Max temperature and max temperature difference is the most important results of the thermal analysis. The program suggests that it is safe to maintain a maximum temperature below 158 °F (70 °C). The maximum temperature difference is safe to maintain below 35 °F (20°C) degrees. Users can try different starting times and placing temperatures to get the least peak temperature as well as the least temperature different.

More than 19 degrees of the temperature difference between internal and surface temperatures of concrete is considered as critical by the program. As a rule of thumb, we consider the temperature difference below 20 degrees between core and surface is ok.

On most occasions, cracks develop at night due to the lowest surface temperature. In these kinds of situations, wooden forms and covering blankets act as thermal dampers. They maintain a temperature difference across the material keeping the concrete warm. That way we can control the maximum temperature difference, however, it will affect the peak temperature. The more you keep the heat energy inside, the core temperature increases.

Heating the concrete more than 158 °F (70 °C) can lead to delayed ettringite formation and ultimately cracks the concrete. Therefore the cracking possibility of concrete due to heat of hydration should be closely analyzed well before the placement and reduce the risk as much as possible.

ConcreteWorks program is a powerful tool to understand the effect of each parameter on the peak hydration temperature of concrete. Let’s see a simple trial on checking the effect of placing temperature on the peak hydration temperature of the concrete.

Initial data

Member type

  • Mass concrete

General inputs

  • English units
  • 31st October 2020, 8 am
  • Temperature analysis for 7 days
  • State: Texas, City: Houston

Shape inputs

  • Rectangular footing

Member dimensions

  • 15 ft × 15 ft × 3 ft
  • Fully submerged condition
  • 2-D analysis

Mix proportions

  • Default mix
Cement content564 lb/yd3
Water content220 lb/yd3
Coarse aggregate content1800 lb/yd3
Fine aggregate content1100 lb/yd3
Air content5%
Default mix proportion

Material properties

  • Cement type I/II
  • Coarse aggregate: Limestone
  • Fine aggregate: Siliceous river sand

Mechanical properties

  • Nurse – Saul method

Construction inputs

  • Concrete fresh temperature equals ambient temperature
  • Forms remove after 96hrs
  • Form type: Wood
  • Soil, water temperature: 80 °F
  • Sub-base: limestone
  • Curing blankets: clear plastic sheet at 5hrs time

Environmental inputs – Use default

Corrosion inputs – Use default

Results

Placing temperature (°F)Peak temperature difference (°F)
6046
6852
7759
8666
Placing temperature and corresponding peak hydration temperature

The analysis gives you what could be the maximum temperature and maximum temperature difference in and out of the concrete. Obviously, the peak temperature difference increases with the placing temperature. So, to reduce the temperature difference, one of the direct approaches is reducing the placing temperature.

The use of chill water, ice, and pre-cooling the materials are the best and common ways of reducing the fresh concrete temperature. However, there are some indirect solutions to this problem.

Adjusting the starting time.

By adjusting the starting time of the concrete, we can alter the peak temperature. This results in reducing the temperature difference too. The program allows you to try out different placing times as well as days for the analysis and select a suitable time for the work. The above example uses 7 am as the starting time of the concrete. The following results show the peak heat difference in case if the same work started at 7 pm.

Concrete started at 7 am Peak temperature difference (°F)Concrete started at 7 pm Peak temperature difference (°F)
4643
5249
5956
6662
comparison of peak hydration temperature under different placing times

It clearly shows that low cracking risk is available when concreting at night time.

Adding fly ash

The addition of fly ash is an easy and economical solution for high hydration temperature issues in concrete. Fly ash reduces the hydration rate of the concrete. This will allows the concrete to dissipate the heat energy longer and reduce the maximum temperature.

Let’s assume 20% cement replacement by class c fly ash for the analysis. The program clearly reduces the peak temperatures with fly ash addition.

100 % cement80 % cement + 20 % fly ash
4642
5247
5953
6660
Effect of fly ash addition on peak hydration temperature difference

Likewise, we can use this program to analyze the effect of each parameter on the peak hydration temperature of different types of concretes

kalhara

Kalhara Jayasinghe is a civil engineer currently engage with hydropower construction works in Sri Lanka. He has completed his bachelor's degree & master's in structural engineering from the University of Peradeniya and achieved chartered engineer title in 2019 from the Institute of Engineers Sri Lanka.

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