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.
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
The program offers several unique shapes under different member types you selected. The summary of all the shapes is tabulated below.
| Mass concrete | Bridge Deck | Precast concrete | Pavements |
| Rectangular column | Deck with precast panel | Box beam (type 5B40) | Rectangular cross-section |
| Rectangular footing | Deck with a metal pan as a formwork | Type IV – I beam | |
| Partially submerged rectangular footing | Deck made with removable wooden formwork | U 40 Beam | |
| Rectangular bent cap | Generic user-defined bridge | U 54 Beam | |
| Circular column |
Member dimensions
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
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
This window collects the material properties using in the mix. Cement type and chemical composition are according to the manufactures datasheet.
| Cement type | Cement | Application |
| Type I/II | Either type I or type II (both are acceptable) | No or moderate sulfate resistance |
| Type I | Portland cement | General-purpose (no special properties required) |
| Type II | Portland composite cement with addition exceeding 5% | Moderate sulfate resistance |
| Type V | Composite cement | High sulfate resistance |
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
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
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.
Environmental inputs
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
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.
| Parameter | Most suitable range |
| Rectangular Column Width or Depth | 3 ft ~ 30 ft |
| Rectangular Footing Width, Length | 3 ft ~ 80 ft |
| Rectangular Footing Depth | 3 ft ~ 30 ft |
| Rectangular Bent Cap Width or Depth | 3 ft ~ 30 ft |
| T-Shaped Bent Cap Width | 3 ft ~ 15 ft |
| T-Shaped Bent Cap Height | 3 ft ~ 15 ft |
| Circular Column Diameter | 3 ft ~ 15 ft |
| Cement Content | 100 # ~ 1200 # |
| Water Content | 100 # ~ 1200 # |
| Coarse Aggregate Content | 100 # ~ 4000 # |
| Fine Aggregate Content | 100 # ~ 4000 # |
| Air Content | 0% ~10% |
| Class C Fly Ash Content | 0 # ~ 1200 # |
| Class C Fly Ash CaO | 20 % ~ 30 % |
| Class F Fly Ash Content | 0 # ~ 1200 # |
| Class F Fly Ash CaO | 0 % ~ 20 % |
| Slag Content | 0 # ~ 1200 # |
| Silica Fume Content | 0 # ~ 1200 # |
| Ultra-Fine Fly Ash | 0 # ~ 1200 # |
| Any Bogue Compound Content | 0 % ~ 100 % |
| Any Bogue Compound that does not meet ASTM C 150 | |
| C3A | 1% |
| Blaine Fineness | 280 kg/m3 ~ 1000 kg/m3 |
| Alkali Content | 0% ~ 100% |
| Fresh Concrete Placement Temperature | 32 °F ~ 212 °F |
| PCC age at form removal | 0 hrs |
| The delay between removing forms and cure method application | 0 |
| Hydration Parameter alpha | 0 ~ 1 |
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 content | 564 lb/yd3 |
| Water content | 220 lb/yd3 |
| Coarse aggregate content | 1800 lb/yd3 |
| Fine aggregate content | 1100 lb/yd3 |
| Air content | 5% |
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) |
| 60 | 46 |
| 68 | 52 |
| 77 | 59 |
| 86 | 66 |
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) |
| 46 | 43 |
| 52 | 49 |
| 59 | 56 |
| 66 | 62 |
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 % cement | 80 % cement + 20 % fly ash |
| 46 | 42 |
| 52 | 47 |
| 59 | 53 |
| 66 | 60 |
Likewise, we can use this program to analyze the effect of each parameter on the peak hydration temperature of different types of concretes
