Code from: The climate benefits from cement carbonation are being overestimated

https://doi.org/10.5061/dryad.6hdr7sr7n

Title of Dataset: "CO2uptake_with_mortar.m"

Author Information

Elisabeth Van Roijen
University of California, Davis
Email: evanroijen@ucdavis.edu

The enclosed files contain the data and code scripts used that can be used to reproduce results from the associated publication, “The climate benefits from cement carbonation are being overestimated”.

This code calls to data in the attached excel spreadsheets "Supplemental Data_v3.xlsx", and they must be in the same folder to work.

Approximate date of data collection: 2021-2023.

Sharing/access information

All data sources are described in the methods and supplemental materials of the publication: “The climate benefits from cement carbonation are being overestimated”, DOI (https://doi.org/10.1038/s41467-024-48965-z).

Code/Software

Codes presented in this work are written in Matlab script. They operate on Matlab R2023a, and no non-standard hardware is required. Scripts call to data as presented in the supplementary data sheets of the associated article, as well as an additional excel sheet ìCO2_profile_V1î. Data and codes must be in the same folder to run. As this is a code, not a software, there is no typical install time. Runtime is a few seconds on a normal computer.

Goal and scope of code

Description: this code uses a fixed set of parameters to determine the emissions and carbon uptake associated with concrete consumption in the United States as well as globally, utilizing data from the years 1900-2025 and 1930-2050, respectively. The output of this code is a three-panel figure (similar to Figure 3 seen in the manuscript "The climate benefits of cement carbonation are being over-estimated").

How it works

Section 1: "INPUTS"
This section calls to the supplementary data file to collect data such as the years being examined (denoted as variable "years"), cement content in concrete (Ci, in units of kg cement/m3 concrete), cement consumption in kg cement/year (C_cons), emissions from cement consumption in kg co2/yr (C_emiss), the cumulative radiative forcing of cement emissions (emiss_CRF), the cumulative radiative forcing of carbon uptake per year (uptake_CRF), and the net cumulative radiative forcing (net_CRF) that simply sums the CRF of emissions and uptake. Note that the "years" for CRF data continue for an extra 100 years, this is to capture the effects of CO2 emissions that are emitted in the last year of cement consumption (noting the lifetime of CO2 in the atmosphere is 100 years). Additionally, the fraction of cement used in concrete (P_con) vs mortar (P_mortar) is defined. From here, yearly cement production for concrete and mortar is calculated (Cons_conc and Cons_mortar, respectively).

Section 2: "CEMENT LIFETIME"
This section of the code collects data on the lifetime of cement. "P_enduse" holds data for the percent of cement used in civil engineering, residential and non-residential applications. "t_enduse" holds data for the lifetime of cement in each of the end-use categories. Finally, "Tk" holds data for the thickness of concrete in each end-use category/application. The end-of-life phase is held constant at 0.4 years (the global average demolition phase value), and secondary life is assumed to be 35 years. The length of each of these stages (in years) is stored in the variable "duration". Finally, to determine the quantity of cement in each end-use category ("concrete_enduse"), "C_cons" is multiplied by "P_enduse".

Section 3: "MODIFICATIONS"
This section lays out the assumptions for the carbonation process for cement. Note that these variables can be altered, and the effects can be examined in the other code supplied, entitled "Master_uptake_kg". "type_scm" defines the type of supplemental cementitious material (SCM) in the cement. For the global and United states assessment, no SCMs were assumed to be present. As a result, "precent_scm" was set to zero. "diameter" defines the diameter (in mm) of concrete particles at end-of-life. In the global and US models, the range is assumed to be 1-40mm. Three variables are used to define the carbonation coefficients, namely (1) "exposure" (B_ec) which can either be exposed, buried, indoors, sheltered, or wet (2) "coating" (B_cc) wherein options include no coating, indoor coating, and painted infrastructure, and (3) "location" (B_CO2) which can either be urban, rural, seaside, industrial, road or buried. If an SCM is assumed to be included in cement, then an additional carbonation factor (B_ad) specifying the type of SCM should be incorporated. For the US and global models, concrete is assumed to be exposed during useful life and demolition and buried during end-of-life. Concrete is assumed to have no coatings during all lifecycle stages. Finally, the location is assumed to be urban during useful life, industrial during end-of-life, and road during secondary life. To store the results, the rows and columns of the variable "concrete_enduse" are saved as "nyears" and "n_enduse", respectively. Further, the length of each lifecycle stage in years is determined based on input data ("td_yrs"), the length of the demolition phase (td) can be entered using decimals whereas the useful life (tl) and secondary life (ts) must be inputted as integers.

Section 4: "Service life stage"
Using the variables defined above, this section calculates the carbon uptake occurring during the useful life of cement by first calculating the carbonation rate coefficient (kli). Then the carbonation depth (dli) is calculated using Fick's law of diffusion. From here, the volume of carbonated concrete (Vi) can be calculated by combining the carbonation depth, weight of cement consumed (Wci), cement content of concrete (Ci) and thickness of concrete. The cumulative mass of carbonated cement (Wli) can then be calculated by summing up the annual quantities (del_Wli). Finally, the mass of CO2 absorbed during the useful life of cement (Cl)is calculated by multiplying the mass of carbonated cement by the clinker to cement ratio (Cclinker), the CaO content of clinker in cement (fCaO), the proportion of CaO within fully carbonated cement that converts to CaCo3 (gamma), and ratio of the molar mass of CO2 to Cao (Mr).

Section 5: "Demolition stage"
The above process is repeated to determine carbon uptake occurring at end-of-life. The only difference is the value of the carbonation coefficient at end-of-life (kdi), which is calculated based on the environmental conditions assumed to take place at that time. This carbonation coefficient is used to determine the depth of carbonation of concrete at end of life (ddi) once again using Fick's law of diffusion. The maximum diameter of particles undergoing carbonation (D0i) is calculated. Further, the fraction of carbonated demolished concrete (Fdi), is calculated assuming demolished concrete is in the shape of a sphere. From here, the mass of concrete reaching end-of-life (Wdi) is used to determine the weight of carbonated concrete at end-of-life (Wd). From here, the total mass of carbon uptake occurring during end-of-life (Cd), and the quantity of carbon uptake occurring each year (del_Cd), if the demolition phase is longer than a year, is determined. Note that emissions from demolition processes(demolition_emissions) such as fuel combustion for crushing concrete particles, is included in this calculation.

Section 6: "Secondary life stage"
The process used to determine carbon uptake during useful life is repeated to determine carbon uptake occurring during the secondary life. The only difference is the value of the carbonation coefficient (ksi). Using this, along with the mass of cement reaching secondary life (Wsi),the total carbonation depth (dti), the maximum particle diameter (Dli) of fully carbonated concrete, the fraction of carbonized cement (Fsi), the cumulative mass of carbonated cement (Ws), and the mass of cement carbonated during secondary life (Cs) is calculated.

Section 7: "Total: carbon uptake by concrete cements"
In this section, the total mass of carbon uptake throughout the lifecycle of cement (C_con) is determined by summing up carbon uptake during end-of-life and secondary life (C_EoL), as well as the useful life (del_Cl).

Section 8: "carbon uptake by mortar cements"
This section of the code calculates the carbon uptake occurring in cement that is used in mortar applications. This is broken down into different types of mortar cement. Namely rendering, maintaining/repairing, and masonry. The fraction of mortar cement used in each application is saved in the variable "m_enduse". The mass of mortar in each end-use category (mortar_enduse_r, mortar_enduse_m, and mortar_enduse_ma for rendering, maintenance and masonry, respectively) is calculated using these fractions, along with the total mass of cement used in mortar applications. The mass of SCMs, if applicable, may then be incorporated to determine the mass of mortar (Wri, Wmi, and Wmai for rendering, maintenance and masonry, respectively). The carbonation coefficient for mortar (Km), is assumed to be the same as concrete. However, the average cement content in mortar is re-defined (using Ci) since it differs from cement content in concrete. The thicknesses of mortar in each application are also defined (expressed in the variables "dTrp"). The proportion of CaO within fully carbonated mortar cement that converts to CaO is defined using the variable "gamma1". Finally, the carbonation rate coefficients associated with different exposure conditions are defined. From here, the quantity of CO2 taken up in mortar cement is calculated the same way as previously described for cement in concrete. With Vri, Vmi, Vmai, being the volume of carbonated mortar, Wri, Wrmi, and Wrmai, being the mass of carbonated mortar, and Crp, Crm, and Crma, being the mass of carbon taken up during the lifetime of mortar in rendering, maintenance, and masonry applications, respectively. Finally, the total mass of carbon uptake for all mortar applications is calculated (C_mor), as well as the annual carbon uptake for mortar applications (Del_C_mor)

Section 9: "total uptake concrete + mortar"
This section adds together the carbon uptake occurring in concrete and mortar to determine total carbon uptake for all cement each year ("annual_uptake"), as well as the net emissions which includes production emission of cement ("net").

Section 10: "FIGURES"
This section outputs Figure 3 in the manuscript "The climate benefits of cement carbonation are being over-estimated". Note that the axes and data used to make the figure can either call to global data, or US data. Be sure to toggle off the dataset that is not being plotted.