loss of air content in pumped concrete what why how Related Information

Understanding Wet-Mix Shotcrete: Mix Design

Initial Air Content concept. This concept is a . clever and simple system by which the workability of the fresh concrete is increased to meet the pump-ability requirement by introducing a large amount of entrained air bubbles into the mix, instead of relying on water-reducing admixtures to increase workability. The trick is that during pumping and

Air Entrainment - an overview | ScienceDirect Topics

M Richardson, in Durability of Concrete and Cement Composites, 2007. Allowance for strength loss. Air entrainment leads to a loss of concrete strength. Typically the direct strength loss is about 5.5% per percentage of air entrainment though this effect can be somewhat offset by the improved workability (reduced water demand) of air entrained concrete (Wright, 1953).

Loss of Air Content in Pumped Concrete - Atlantic Concrete

Oct 01, 1992 · Describes an investigation of the phenomenon of loss of entrained air in pumped concrete. Conclusions and recommendations include: 1) With long vertically downward boom or pipe sections, half the air can be lost; 2) Do some sampling at the pump discharge; 3) If air is lost, fix the problem.

Loss of Air Content in Pumped Concrete

Keep concrete from sliding down the line under its own weight. Where possit;>le, avoid vertical or steep downward boom sections. Be cautious with higslumps, particularly with 3 high cement content mixes and mixes containing silica fume. Steady pumping may help somewhat to minimize air loss…

CIP 21 - Loss of Air Content in Pumped Concrete

2. WHY is Air Lost? There are several mechanisms involved, but air loss will occur if the weight of concrete in a vertical or near vertical downward pipe is sufficient to overcome frictional resistance and let a slug of concrete slide down the p ipe. One part of the theory is …

Pumping of Concrete

These pumps are capable of pumping 130 m3 of concrete per hour with 8 inch pipes. Squeeze pumps or peristaltic pumps are the ones that use vacuum pumping. These pumps can cover a distance of 90 m horizontally and 30 m vertically, and are capable of pumping 20 m3 of concrete per hour using 3 inch pipes. (a) Direct acting piston pump.

Factors affecting durability of concrete • Aggregate

Jan 27, 2010 · Concrete with a low water-cementitious ratio (0.40 or lower) is more durable than concrete with a high water-cementitious ratio (0.50 or higher). Air-entrained concrete with a low water-cementitious ratio and an air content of 5 to 8% will withstand a great number of cycles of freezing and thawing without distress.

PROPERTIES AND MIX DESIGNATIONS

5-694.216 AIR ENTRAINMENT All concrete contains some entrapped air bubbles. Large entrapped air bubbles are undesirable. Air-entrained concrete has air, in a finely divided and dispersed form, purposely induced at the time of mixing. The air is produced in the concre te by the addition of an approved air-entraining admixture.

CIP 21 - Loss of Air Content in Pumped Concrete

Increasingly, specifiers are requiring concrete to be tested for air content at the discharge end of concrete pumps at the point of placement in the concrete struc-ture. In some cases it is observed that air contents are much lower than that in samples tested at discharge from the truck chute. It is normal to find a loss of about 0.5 to 1.0 percent air as concrete is conveyed through a pump.

Concrete Pump Blockage - Causes & Clearing - Concrete Network

Pipes that have been improperly cleaned may cause blockages where old concrete has set and may cause bleeding and segregation. Defective couplings, gaskets, or weld collars also can result in the loss of grout. Another thing to look for are bends that are too short, too sharp, or too numerous, all of which increase concrete pumping pressure.

CONCRETE 101

specification requirements which require a specific amount of air content at the point of placement or at the discharge end of the pumping. Air loss can be minimized when pumping by slowing down the "free-fall" of the concrete and minimizing the pumping pressure. 2. What is slump? (Why/what/how it effects concrete and us)

A Review of ACI 301 Section 4, Concrete Mixtures

Exposure class Maximum w/cm Minimum f' c, psi Air Content Additional requirements 4.5 Exposure Class F2 and F3 3/8" 6.0 5.0 Air Content 1" 6.0 1-1/2" 5.5 4.5 Air Content Exposure Class F1 6.0 5.5 TABLE 4.2.2.1.b.1 — Total air content for concrete exposed to cycles of freezing and thawing 3/4" 7.5 1/2" Nominal maximum size of aggregate, in. 7.0

Factors affecting durability of concrete • Aggregate

Jan 27, 2010 · Concrete with a low water-cementitious ratio (0.40 or lower) is more durable than concrete with a high water-cementitious ratio (0.50 or higher). Air-entrained concrete with a low water-cementitious ratio and an air content of 5 to 8% will withstand a great number of cycles of freezing and thawing without distress.

Mix Design and Pumped Concrete - Civil Engineering Portal

A loss of slump during pumping is normal and should be taken into consideration when proportioning the concrete mixes. A slump loss of 25 mm per 300 meters of conduit length is not unusual, the amount depending upon ambient temperature, length of line, pressure used to move the concrete, moisture content of aggregate at the time of mixing

Batching, Mixing, Transporting, and Handling Concrete

time, about 1 or more hours, can result in concrete strength loss, temperature rise, excessive loss of entrained air, and accelerated slump loss. When truck mixers are used, ASTM C 94 (AASHTO M 157) also limits the time between batching and complete discharge of the concrete at the job site; this time is 1. 1 ⁄ 2

CIP 21: Loss of Air Content in Pumped Concrete - Kentucky

Kentucky Concrete Association 1 HMB Circle Frankfort, KY 40601 502 695-1535 [email protected]

Volume 19/Number 1 Control of Air Content in Concrete

Control of Air Content in Concrete Air-Void Analyzer Figure 1. Freeze-thaw deterioration of non-air-entrained concrete railing. (S44517) Control of Air Content in Concrete New manual provides concrete producers and users with tips on achieving and controlling air in concrete. Air entrainment is a necessary com-ponent of concrete mixtures exposed

A Contractor's Guide to Superplasticizers

Fi g u r e 1 shows slump loss at va r i-ous mixing times of concre t e s t reated with different superplasti-c i ze r s. In the 90-minute time f ra m e, the smallest slump loss is 1 inch compared to the larg e s t slump loss of over 4 inches. References 1. ACI 212R-91,"Chemical Admixtures for Concrete," Manual of Concrete

ASTM C231: Testing Air Content of Concrete With a Type B

Apr 04, 2021 · Significance and Use of ASTM C231. This test's purpose is to get the air content of a sample of concrete using a pressure meter. In the meter you have a known volume of air at a known pressure in a sealed air pot with an unknown volume of air being contained inside the sample of wet concrete.

Mix Design and Pumped Concrete - Civil Engineering Portal

A loss of slump during pumping is normal and should be taken into consideration when proportioning the concrete mixes. A slump loss of 25 mm per 300 meters of conduit length is not unusual, the amount depending upon ambient temperature, length of line, pressure used to move the concrete, moisture content of aggregate at the time of mixing