Concrete Supply Options in Remote Locations for ...tsdos.org/media/presentation2019/Schrein,...

SEPTEMBER 4 - 6, 2019

Concrete Supply Options in Remote Locations for Transmission Lines &

Substations


INTRODUCTION• UTILITY SYSTEM GROWTH

– REMOTE LOCATIONS

– LOW POPULATION DENSITY

– LITTLE INFRASTRUCTURE

• CONC. SUPPLY IN REMOTE LOCATIONS

– FEW SUPPLIERS

– LONG DISTANCES

– DIFFICULT DELIVERY

– UNRELIABLE OR INCONSISTENT SUPPLY


VOLUMETRIC BATCHING


TYPICAL EQUIPMENT ARRANGEMENT• Common names:

– Concrete mobiles– Mobile mixers– Shake and Bake trucks

• Truck / Trailer-mounted

• Variety of tanks and bins

– Sand– Coarse aggregate– Cement– Water– Admixtures


SAND & GRAVEL BINS

WATER TANK

CEMENT COMPARTMENT

ADMIXTURES RESERVOIRS


LIMITATIONS• Single bin for the cementitious material.

– Sealed in order to prevent moisture

infiltration

– More difficult to incorporate

supplementary cementitious material

(fly ash, ground granulated slag)

• Quantity of on-board materials –

continuous supply an option


ADVANTAGES• On-site concrete production for foundations

– Transport time no longer a concern

– Temperature less of a concern

• Dedicated, uninterrupted concrete supply

– Dedicated equipment and materials

– High-demand regions - difficult to guarantee concrete availability

• Reduced concrete waste

– Limits the need for concrete washout areas

– Traditional ready-mix plant may require a min. order


ADVANTAGES• Specialty concrete mix capability

– Coloring, fiber reinforcement,

or other admixtures

• Reduced concrete costs

– Concrete costs may be

reduced by ~40%

– Primarily from the prevention

of over-ordering


DISADVANTAGES• Less consistency

– Shown to have a higher variability in testing

• More frequent strength testing per ASTM C685

• Small volume of concrete production

– Capacity 3 to 12 CY per truck (8-9 CY for a legal load)

– Production rates of 30 to 90 cubic yards per hour

• On-site storage of constituent materials

– Stockpile of materials to facilitate continuous production of concrete


CALIBRATION/QUALITY CONTROL• Testing

– Calibration & Efficiency Tests - every 6 mo or less per

ASTM C685

– Uniformity Test - TxDOT TEX-472-A

– Strength Testing - every 25 cubic yards

• Operator Qualification (ACI 304.6R)

– Manufacturer training and certification suggested

– On-the-job training - minimum of 4 weeks


READY-MIX BATCHING


TYPICAL EQUIPMENT ARRANGEMENT• Permanent stationary facility

– Weigh batcher– Aggregate storage

pits/bins– Silos for cementitious

materials– Washouts– Control building

• Constant supply of material


TYPICAL EQUIPMENT ARRANGEMENT• Operation

– Dry material measured on calibrated scales

– Admixtures and water dispensed by calibrated flow meters

– Mixing process occurs in transit mixer trucks unless the batch plant is a central mixing unit

– Constituents are added via computer-controlled sequencing

– Batch ticket is created• target/actual mix design

material amounts


EXTENDED HAUL TECHNIQUES• Typical concrete load

– Approx. 1.5-2 hours for delivery and placement

• Can be delivered long distance or extended duration

– Requires pre-planning, trial batches, slump loss testing, and proper sequencing

– Slump, concrete temperature, and air content are all affected

– Concrete temperature influences slump and slump loss

– Admixtures are time sensitive

75

80

85

90

95

0

2

4

6

8

10

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5

TEM

PERA

TURE

(DEG

F)

SLU

MP

(IN) /

AIR

CON

TEN

T (%

)

TIME (HOURS)

Example Slump Loss Test

Slump Air Content Temperature


EXTENDED HAUL TECHNIQUES• Control cement hydration

– Hydration controllers, hydration stabilizers, retarding agents

– Dosage affects the duration• Slump control

– by water, water-reducing agents, or high-range water reducers (also referred to as superplasticizers)

• Temperature control– by chilled water, ice, liquid nitrogen,

aggregate cooling • Field addition of air entrainment is

common practice to raise air content


ADVANTAGES• Calibrated weigh batching

equipment

– Accuracy (+/-0.4% of load)

• Wide range of available admixtures

– Aid in long-haul concrete delivery

• Easier incorporation of SCM’s 0

2000

4000

6000

8000

10000

12000

COM

PRES

SIVE

STR

ENGT

H (P

SI)

Example-Volumetric vs Weigh Batchingfc' = 4000 psi Volumetric Weigh


DISADVANTAGES• Concrete waste

– Over-ordering of concrete

• Concrete delay and interruption

– Under-ordering, or traffic

delays

– Costly repairs or cold joints

• Admixtures can be cost

prohibitive

• Off-hours availability, undedicated


PORTABLE BATCH PLANT


CONSIDERATIONS• Job size will determine portable

batch plant feasibility• Should go through a typical plant

certification, such as the NRMCAPlant Certification

• Can be volumetric or weigh batching• Generally has the same capabilities

as a ready-mix facility• May require additional permitting• Need power and water brought in


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Concrete Supply Options in Remote Locations for ...tsdos.org/media/presentation2019/Schrein,...

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