JOB MIX FORMULA PROCESS (PREMIX)

Upon receiving an approved mix design, the Resident Engineer shall forward it to the contractor and request the contractor propose a job-mix formula(JMF). The contractor will submit his proposed JMF to the Resident Engineer for review and approval. After reviewing the proposed JMF and making any necessary corrections, the Resident Engineer will establish the approved JMF and send it to the contractor. The Resident Engineer will also send copies the approved JMF to the SO and SO representative. When distributing the approved JMF, it is helpful to attach a copy of the approved mix design.

The first JMF should be JMF No.1. Sebsequent JMS's must be issued if there is a change in any item shown. Additional JMF's will be numbered with the next subsequent number (i.e, 2, 3, 4, 5,..). When a JMF has been distributed with typos and/or error, the corrected JMF will be a revised JMF. The JMF number will not change. However, a letter "R" will be added to the number (i.e, 1R, 2R, 3R,..). After JMF No. 1, any required changes and/or revision should be in bold for easy identification.

Contoh 1 : The Resident Engineer completed and distributed JMF No. 1 based on the approved mix design. However, recent test results indicate he needs to adjust the combined percent passing target and job-mix range for two sieves. The Resident Engineer will change the combined percent passing targets on the two sieves and adjust the job-mix range accordingly.
This job-mix will be JMF No.2

Contoh 2 : The Resident Engineer completed and distributed JMF No. 1 based on the approved mix design and later notices that it has the incorrect bitumen ratio. The Resident Engineer will revise the JMF to reflect the correct bitumen ratio and redistribute the JMF as JMF No 1R

Note : Every contract will have its own set of JMF No's. for each approved mix design

Prescribed Mix - Compliance Requirement

Production & Supply Concrete To Site

The Parameters used in the trial mix must be maintained during actual production & supply concrete to the site. Adjustment are allowed within Cl. 3.2.4

It is the responsibility of the Contractor to ensure the supplier produce and deliver to the site, concrete in compliance with the requirements of the specifications and providing information as required by SPK

However, for the smooth flowing of concrete works at the site, the following process of approval and verification shall be clarified and agreed upon between S.O and Contractor. (* Delete where applicable)

1. Batching Plant : The Contractor shall ensure his supplier permits access for the S.O to enter the premises periodically to inspect the production of concrete.

2. Delivery Note : The time of batching for all concrete delivered to site shall be noted. Maximum allowable duration is Two Hours (2 jam). Concrete must immediately be rejected after the expiry of this duration. ( Nota : Duration of 2 hours means the time between batching and completion of placing vibrated concrete)

3. Batching Record : For every load of concrete delivered to Site and shall be given to the Contractor and jointly verified for compliances by the S.O. *during delivery / at the end of the day's concreting / within 2 days

4. Workability : Verification of every load of concrete is by slump test. * truck driver / Contractor / S.O shall carry out the test and verified for placement or reject by * Contractor / S.O

5. Test Cubes : Prepared by * truck driver / Contractor / S.O. Record and markings by *truck driver / Contractor/S.O Must be cured and kept in curing bed constructed at/near S.O's site office. Testing at *supplier's lab / IKRAM / Independent lab. Testing witnessed, verified and recorded by *S.O, Contractor & Supplier / Contractor & Supplier / Supplier only. Test must be carried out at the 7th and 28th day.

6. Additional Cubes : For earlier removal of forms other than specified in Table 10 or for pre-stressed concrete before transfer. However, Cl 4.9 & 8.4 must be complied. Two cubes required from each sample (nota: The curing of the cube shall not followthe normal condition but to simulate the actual field condition and kept separately from the curing bed)

7. Rate of Sampling : Must comply with Cl 4.3. Three (3) cubes taken from each sample. One(1) tested for 7 day strength and Two(2) for 28 day strength. First day of concreting, twelve (12) cubes from four (4) samples must be taken regardless of volume for each grade of concrete.

8. Tempreture : Cl 5.6 shall be observed. For Cl. 5.5-c *plastic sheet / tarpaulin shall be used for cast in-situ slabs, prestressed slab, slab toppings, cast insitu beams and post tensioned beams.

9. Curing & Protection : Must start by final set time of concrete ie 600min. Method of curing is by *wet gunny sack / impermeable sheeting / continuous wetting of surface / membrane forming curing compound. Curing period shall not less than 5 days.

Trial Mix

Refer to Previous Table

Trial Mix must be witnessed and verified by the S.O and conforming with MS 26 and Cl. 3.2.3-Section D. Informations must be recorded using the relevant Borang SPK.

• If a current marging of 12 N/mm2 ia adopted. The Target Mean Strength = 52 N/mm2. The average 28-day strength from the nine (9) cubes obtained from the three (3) batches of concrete shall exceed (52-3.5) N/mm2 i.e 48.5N/mm2

• The S.O shall give the approval in writing

Trial Mix (Contoh Perkiraan)

1. Nilai purata konkrit, fm = 46.8 N/mm²

2. Jidar semasa(Current Margin) = 7.5 N/mm²

* Pensampelan dan prosedur ujian hendaklah berdasarkan kepada MS 26 atau BS1881

* Purata kekuatan konkrit berdasarkan kepada keputusan ujian mampatan bagi 9 kiub pada hari ke 28 > atau = gred + jidar semasa - 3.5 N/mm² (cl 3.2.3)

3. fm (campuran semasa) = 40 + 7.5 - 3.5 = 44.0 N/mm² < 46.8 N/mm²

4. Ujian ini berjaya dan kerja-kerja konkrit boleh diteruskan dengan syarat nisbah campuran dan bahan (materials) yang digunakan semasa bekalan ke tapak adalah sama dengan yang digunakan semasa "Trial mix" ini.