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POINT OF VIEW

3. Material Handling and Hydraulic Systems: Efficient mixer within 2 hours of the time of loading. However, a longer
material handling is critical for the performance of period may be permitted if retarding admixtures are used or in
volumetric mixers. They are provided with automated cool humid weather or when chilled concrete is produced.
gates and feeds, which are controlled digitally, and
manage material flow into the mixing chamber quickly As per clause 5.2.2.2 the time of loading shall start from adding
and precisely. In addition, advanced hydraulic and motor the mixing water to the dry mix of cement and aggregate
systems allow for the adjustment of mixing speeds to or of adding the cement to the wet aggregate whichever is
accommodate different concrete mixes and applications, applicable.
ensuring consistency and quality.
In addition, clause 9.1.4.3 on truck mixers states that in order to
By leveraging these advanced technologies, volumetric produce a satisfactory mix, and where there is no data available
mixers not only enhance the quality of the delivered concrete to establish different period and speed of revolutions, mixing
but also offer increased flexibility and efficiency on-site. shall continue for not less than 60 revolutions of the truck mixer
The improvements in sensor technology, real-time data drum at a rate of not less than 7 revolutions/min. All completely
communication, and hydraulic systems collectively contribute to truck mixed concrete shall be visually inspected for uniformity
a more reliable and adaptable concrete delivery process. prior to leaving the plant. When a truck mixer or agitator is used
for transporting concrete which has been mixed before leaving
7. THE BENEFITS TO THE CONCRETE the plant, the concrete shall be agitated during transit and re-
mixed at the site for at least 2 minute so that the concrete is of
INDUSTRY
the required uniformity.
[4]
A change in the ASTM C94-21 which removes time limit to
discharge concrete would greatly benefit all involved with Unfortunately, some large organizations and their specifications
placing concrete. For the concrete pumping companies, it would in India, are still following the 90 minute rule. If concrete
allow them greater latitude to remedy problems they may arise: placement is delayed by even a minute, the concrete is rejected
before the pour (traffic, flat tire), during prime out, equipment by these organizations, regardless of its quality, resulting in
failure, etc. Often, the stress and hurriedness associated wastage of material, cost, time, and labor.
with supplying the concrete, quickly, in order to comply with
the 90 minutes rule, may lead to shortcuts and unintended 9. CONCLUSION
consequences resulting in accidents. Ready mixed concrete
companies may also be benefitted from having to remove and Extended delivery times (instead of the 90 minutes specified
dispose the returned concrete, which can be extremely costly in earlier ASTM C 94), supported by advances in concrete
and non-productive. technology, offer producers and purchasers greater flexibility
[14]
and sustainability. The Indian code IS: 4926 (2003) on RMC
Time limit leniency would allow contractors to have greater allows 2 hours or even extended time, if retarding admixtures
control over their projects, eliminate waste and confrontations are used or in cool humid weather or when chilled concrete is
on job sites, and refrain from wasting money on concrete sent produced. A project-specific approach to establishing delivery
back that is perfectly within specifications if it were not for some limits, as advocated by the recent version of ASTM C94 ,
[4]
antiquated standard created 90 years ago. can minimize waste while ensuring that the concrete meets
performance criteria upon placement. Extending discharge
8. ACI COMMITTEE 301 [12] times can provide significant economic and sustainable benefits.
Additionally, the recent advancements in volumetric mixers
ACI Committee 301 is currently reviewing these issues. The will result in the production of quality concrete at the site.
committee, which is responsible for ACI 301–Specifications More discussion on RMC placed after 90/120 minutes and their
for Concrete Construction, is harmonizing the document with advantages are presented in Ref. 15 and 16.
[12]
existing standards (note that ACI 301-20 Section 1.4 references
ASTM C94/C94M-18) . This revision should also be considered
[2]
by the AIA MasterSpec and incorporated into federal and REFERENCES
[13]
state project specifications where discharge time limits are [1] ASTM C94 (1935). “Standard specification for ready-mixed
enforced. concrete,” ASTM International, West Conshohocken, PA,
9 pp.
IS: 4926 (2003) ON READY MIXED-CONCRETE
[2] ASTM C94/C94M (2018). “Standard specification for
[14]
Clause 5.2.2.1 of IS: 4926 (2003) states that the general ready-mixed concrete,” ASTM International, West
requirement is that concrete shall be discharged from the truck- Conshohocken, PA, 2018, 15 pp.

10 THE INDIAN CONCRETE JOURNAL | FEBRUARY 2026