Sec Form 3/A Filing - Grupo Argos S.A. @ Summit Materials, Inc. - 2024-01-12

FORM 3/A Check this box if no longer subject to Section 16. Form 4 or Form 5 obligations may continue. See Instruction 1(b).

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 STATEMENT OF CHANGES IN BENEFICIAL OWNERSHIP Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934, Section 17(a) of the Public Utility Holding Company Act of 1935 or Section 30(h) of the Investment Company Act of 1940

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1. Name and Address of Reporting Person Grupo Argos S.A. 2. Issuer Name and Ticker or Trading Symbol Summit Materials, Inc. [ SUM] 5. Relationship of Reporting Person(s) to Issuer (Check all applicable) X __ Director X __ 10% Owner _____ Officer (give title below) _____ Other (specify below) (Last) (First) (Middle) CARRERA 43A # 1A SUR - 143,, EDIFICIO SANTILLANA, TORRE SUR, PISO 3 3. Date of Earliest Transaction (MM/DD/YY) 01/12/2024 (Street) MEDELLIN, F8050021 4. If Amendment, Date Original Filed (MM/DD/YY) 01/22/2024 6. Individual or Joint/Group Filing (Check Applicable Line) _____ Form filed by One Reporting Person __ X __ Form filed by More than One Reporting Person (City) (State) (Zip)

Table I - Non-Derivative Securities Acquired, Disposed of, or Beneficially Owned 1.Title of Security (Instr. 3) 2. Transaction Date (MM/DD/YY) 2A. Deemed Execution Date, if any (MM/DD/YY) 3. Transaction Code (Instr. 8) 4. Securities Acquired (A) or Disposed of (D) (Instr. 3, 4 and 5) 5. Amount of Securities Beneficially Owned Following Reported Transaction(s) (Instr. 3 and 4) 6. Ownership Form: Direct (D) or Indirect (I) (Instr. 4) 7. Nature of Indirect Beneficial Ownership (Instr. 4) Code V Amount (A) or (D) Price Class A Common Stock ( 1 ) 6,172,416 ( 2 ) I Held by Valle Cement Investments Inc. Class A Common Stock ( 1 ) 48,547,584 ( 3 ) I Held by Argos SEM, LLC Series A Non-Convertible Preferred Stock ( 1 ) 1 ( 4 ) I Held by Cementos Argos S.A.

Table II - Derivative Securities Acquired, Disposed of, or Beneficially Owned ( e.g. , puts, calls, warrants, options, convertible securities) 1. Title of Derivative Security (Instr. 3) 2. Conversion or Exercise Price of Derivative Security 3. Transaction Date (MM/DD/YY) 3A. Deemed Execution Date, if any (MM/DD/YY) 4. Transaction Code (Instr. 8) 5. Number of Derivative Securities Acquired (A) or Disposed of (D) (Instr. 3, 4, and 5) 6. Date Exercisable and Expiration Date (MM/DD/YY) 7. Title and Amount of Underlying Securities (Instr. 3 and 4) 8. Price of Derivative Security (Instr. 5) 9. Number of Derivative Securities Beneficially Owned Following Reported Transaction(s) (Instr. 4) 10. Ownership Form of Derivative Security: Direct (D) or Indirect (I) (Instr. 4) 11. Nature of Indirect Beneficial Ownership (Instr. 4) Code V (A) (D) Date Exercisable Expiration Date Title Amount or Number of Shares

Reporting Owners Reporting Owner Name / Address Relationships Director 10% Owner Officer Other Grupo Argos S.A. CARRERA 43A # 1A SUR - 143, EDIFICIO SANTILLANA, TORRE SUR, PISO 3 MEDELLIN, F8050021 X X Cementos Argos S.A. CARRERA 43A # 1A SUR - 143 CENTRO SANTILLANA, TORRE NORTE, PISO 3 MEDELLIN, E3050021 X X Argos SEM, LLC 251 LITTLE FALLS DRIVE WILMINGTON, DE19808 X X Valle Cement Investments, Inc. CAPITAL PLAZA BUILDING, 15TH FLOOR, PASEO ROBERTO MOTTA, COSTA DEL ESTE PANAMA, R10816-02984 X Signatures /s/ Grupo Argos S.A., By: Rafael Olivella, Title: Vice President 01/26/2024 Signature of Reporting Person Date /s/ Cementos Argos S.A., By: Felipe Aristizabal, Title: Vice President 01/26/2024 Signature of Reporting Person Date /s/ Valle Cement Investments Inc., By: Gustavo Adolfo Uribe, Title: President 01/26/2024 Signature of Reporting Person Date /s/ Argos SEM, LLC, By: Gustavo Adolfo Uribe, Title: President 01/26/2024 Signature of Reporting Person Date

Explanation of Responses:

( 1 )This Form 3 is filed jointly by (i) Grupo Argos S.A., a sociedad anonima incorporated in the Republic of Colombia ("Grupo Argos"), (ii) Cementos Argos S.A., a sociedad anonima incorporated in the Republic of Colombia ("Cementos Argos"), (iii) Argos SEM, LLC, a Delaware limited liability company ("Argos SEM") and (iv) Valle Cement Investments Inc., a sociedad anonima incorporated in the Republic of Panama ("Valle Cement" and collectively with Grupo Argos, Cementos Argos and Argos SEM, the "Reporting Persons"). Each of the Reporting Persons disclaims beneficial ownership of the securities reported herein except to the extent of its pecuniary interest therein. ( 2 )Represents securities of Summit Materials, Inc., a Delaware corporation (the "Issuer"), directly owned by Valle Cement, which is a wholly-owned subsidiary of Cementos Argos S.A., which is a majority-owned subsidiary of Grupo Argos. Grupo Argos, as the controlling shareholder of Cementos Argos, which in turn is the sole shareholder of Valle Cement, has the power to vote and to dispose of the shares of Class A common stock, par value $0.01 per share ("Class A Common Stock"), of the Issuer directly owned by Valle Cement. As a result of this relationship, Grupo Argos may be deemed to be an indirect beneficial owner of the securities that are beneficially owned by Valle Cement. By reason of the provisions of Rule 13d-3 of the Securities Exchange Act of 1934, as amended, each of the Reporting Persons may be deemed to beneficially own the shares of Common Stock of the Issuer directly owned by Valle Cement. ( 3 )Represents securities of the Issuer, directly owned by Argos SEM, which is a wholly-owned subsidiary of Cementos Argos, which is a majority-owned subsidiary of Grupo Argos. Grupo Argos, as the controlling shareholder of Cementos Argos, which in turn is the sole shareholder of Argos SEM, has the power to vote and to dispose of the shares of Class A Common Stock of the Issuer directly owned by Argos SEM. As a result of this relationship, Grupo Argos may be deemed to be an indirect beneficial owner of the securities that are beneficially owned by Argos SEM. By reason of the provisions of Rule 13d-3 of the Securities Exchange Act of 1934, as amended, each of the Reporting Persons may be deemed to beneficially own the shares of Common Stock of the Issuer directly owned by Argos SEM. ( 4 )Represents securities of the Issuer, directly owned by Cementos Argos, which is a majority-owned subsidiary of Grupo Argos. Grupo Argos, as the controlling shareholder of Cementos Argos, has the power to vote and to dispose of the share of Series A Non-Convertible Preferred Stock of the Issuer directly owned by Cementos Argos. As a result of this relationship, Grupo Argos may be deemed to be an indirect beneficial owner of the securities that are beneficially owned by Cementos Argos. By reason of the provisions of Rule 13d- 3 of the Securities Exchange Act of 1934, as amended, each of the Reporting Persons may be deemed to beneficially own the shares of Series A Non-Convertible Preferred Stock of the Issuer directly owned by Cementos Argos.

Remarks: Note: This amendment is being made solely for the purpose of including the additional Reporting Persons, Grupo Argos S.A. and Cementos Argos S.A., as the entities' CIKs were unavailable at the time of filing the original Form 3. Grupo Argos S.A. has been designated the primary Reporting Person in this Form 3/A, which hereby amends and restates the original Form 3, which was timely filed on January 22, 2024, in its entirety.

Reminder: Report on a separate line for each class of securities beneficially owned directly or indirectly.

* If the form is filed by more than one reporting person, see Instruction 4(b)(v).

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