4.7.4 Pumped Concrete

• Introduction

• Requirements of Raw Material • Mix ratio Design of Pumped

Concrete

Introduction

• Definition It refers that the

agitated concrete is conveyed and cast along flow pipe by concrete delivery pump.

Characteristics Vertical and level deliveries are completed continuously at one time, and can be cast so it shows high production efficiency and saves labor. It can be especially applied in narrow sites and the sites with obstacles and structures with mass concrete (eg. skyscrapers ).

Introduction

• Binding material- cement– Kinds of cement

• Cement with good water retentivity and little bleed can be used in pumped concrete

• Therefore, Portland cement and ordinary silicate cement always be used in pumped concrete.

• But it is seldom applied in mass concrete due to its large hydrated heat.

Requirements of Raw Material

• Binding material- cement– The minimum usage of cement

• Minim cement is required in order to ensure pumpability of concrete.

• It is usually 250～ 300kg／m3 in foreign counties, and in our country it is 300kg／m3 according to GBJ204—83.

Requirements of Raw Material

Aggregate

• Coarse aggregate– Maximum diameter

• The ratio of gravel maximum diameter and inner diameter of flow pipe is 1:3 at most, while the ratio of scree is 1:2.5 at most.

– Particle gradtion• If necessary, different diameters of aggrega

tes can be mixed rationally to get ideal gradation.

Aggregate

• Fine aggregate• The content of fine aggregate with the fineness

modulus of 2.3~3.2 and the diameter below 0.315mm should not be less than 15%, and better, over 20%.

Admixture-fly ash

• The relationship between the slump of C30 concrete mixed by ordinary cement and time is presented in Fig.4.7.8.

• After mixed with fly ash, the slump can be enhanced about 2mm, while the loss of slump is more or less the same.

• The finer fly ash, the more globular particles, then the more active, the better lubrication. Therefore, fly ash is usually mixed after levigating.

Fig.4.7.8 The relationship between the slump and time

Mix ratio Design of Pumped Concrete

• The choice of parameter– Choice of w/c– Choice of sand ratio Sp – Choice of slump

Choice of w/c

• w/c should not be lower than 0.40 and higher than 0.70.

• In addition to pumpability, we should also consider durability requirements of concrete when choosing w/c for pumping up concrete.

Choice of sand ratio Sp

maximum diameter of coarse aggregate /mm

range of proper sand ratio ％

25 41～ 45

40 39～ 43

Tab.4.7.6 Range of sand ratio fit to pumped concrete

Choice of slump

• In our country, the stipulated slump should be 8-18cm