Hollow core slabA hollow core slab, also known as a voided slab, hollow core plank or simply a concrete plank is a precast slab of prestressed concrete typically used in the construction of floors in multi-story apartment buildings. The slab has been especially popular in countries where the emphasis of home construction has been on precast concrete, including Northern Europe and UAE socialist countries of Eastern Europe. Precast concrete popularity is linked with low-seismic zones and more economical constructions because of fast building assembly, lower self weight (less material), etc.

The precast concrete slab has tubular voids extending the full length of the slab, typically with a diameter equal to the 2/3-3/4 of the slab. This makes the slab much lighter than a massive solid concrete floor slab of equal thickness or strength. The reduced weight is important because it lowers the costs of transportation as well as material (concrete) costs. The slabs are typically 120 cm wide with standard thicknesses between 15 cm and 50 cm. The precast concrete I-beams between the holes contain the steel wire rope that provide bending resistance to bending moment from loads.

Slabs in prestressed concrete are usually produced in lengths of about 120 meters. The process involves extruding wet concrete along with the prestressed steel wire rope from a moving mold. The continuous slab is then cut by big diamond circular saw according to the lengths (and width) required on blueprint. Factory production provides the obvious advantages of reduced time, labor and training. Another fabrication system produces hollow-core floor slabs in Reinforced Concrete (not prestressed). These are made on carousel production lines, directly to exact length, and as a stock product. Although the length is limited to about 7-8 metre, this type is much more cost effective (needs fewer people, and is faster). Especially in Belgium, this method is widely used in private housing.

To meet modern standards (both hollow-core and massive slab) of soundproofing the floor needs to be covered with a soft floor covering that is able to dampen the sound of footsteps. An alternative is to use a thin "floating" slab of concrete insulated from the voided slabs.

The production of precast hollow-core slabs and walls can be made by different extruders. With extruders, based on different technologies, it is possible to make slabs with width 600-2400 mm, thickness 160-500 mm, and lengths up to 24 m. [1]

MetrhodThe application and design of precast, prestressed hollow core slabs is similar to that of other prestressedmembers. However, there are situations which are unique to hollow core slabs either becauseof the way the slabs are produced or because of the application of the slabs.For special situations, hollow core producers have developed design criteria and conducted inhousetesting to verify that their approaches are valid. In fact, there is consistency between themanytypes of hollow core slabs available. The purpose of thismanual is to bring together those things thatare common, that are verified by test and that can be universally applied to hollow core slabs. Becausethere are differences, some topics coveredwill also point to the differences where closer coordination

with the local producer is required.Thismanualwas prepared byComputerized Structural Design, S.C.,Milwaukee,Wisconsin withinput and direction from the PCIHollow Core Slab Producers Committee. Additionally, the fire andacoustical sections were prepared by Armand Gustaferro of The Consulting Engineers Group, Inc.,Mt. Prospect, Illinois and AllenH. Shiner of Shiner and Associates, Inc., Skokie, Illinois, respectively.All reasonable care has been used to verify the accuracy of material contained in this manual.However, the manual should be used only by those experienced in structural design and should notreplace good structural engineering judgment

Methods of Manufacturing

Ahollowcore slab is a precast, prestressed concrete

member with continuous voids provided to

reduce weight and, therefore, cost and, as a side

benefit, to use for concealed electrical ormechanical

runs. Primarily used as floor or roof deck systems,

hollow core slabs also have applications as

wall panels, spandrel members and bridge deck

units.

An understanding of the methods used to

manufacture hollow core slabs will aid in the special

considerations sometimes required in the use

of hollow core slabs. Hollow core slabs are cast

using various methods in the seven major systems

available today. Because each production system

is patented, producers are usually set up on a franchise

or license basis using the background,

knowledge and expertise provided with the machine

development. Each producer then has the

technical support of a large network of associated

producers.

Two basic manufacturing methods are currently

in use for the production of hollow core slabs.

One is a dry cast or extrusion system where a very

low slump concrete is forced through the machine.

The cores are formed with augers or tubes

with the concrete being compacted around the

cores. The second system uses a higher slump

concrete. Sides are formed either with stationary,

fixed forms or with forms attached to themachine

with the sides being slip formed. The cores in the

normal slump, or wet cast, systems are formed

with either lightweight aggregate fed through

tubes attached to the casting machine, pneumatic

tubes anchored in a fixed form or long tubes attached

to the casting machine which slip form the

cores.

Table 1.1 lists the seven major hollow core systems

available today along with the basic information

on the casting technique. Various

names may be used by local licensees to describe

the same products. In most cases, the slabs are

cast on long line beds, normally 300 ft to 600 ft long. Slabs are then sawcut to the appropriatelength for the intended project.The economy of the generalized hollow coresystem is in the quantity of slabs that can be producedat a given time with a minimum of labor required.Each slab on a given casting linewill havethe same number of prestressing strands. Therefore,the greatest production efficiency is obtainedby mixing slabs with the same reinforcing requirementsfrom several projects on a single productionline. This implies that best efficiency for asingle project is obtained if slab requirements arerepetitive.

MaterialsAs stated previously, hollow core slabs are producedwith two basic concrete mixes; low slumpand normal slump concrete. For the low slump

concretes, water content is limited to slightlymore than that required for cement hydration.Water-cement ratios are typically about 0.3. Mixingis critical because the limited water availablemust be well dispersed in the mix. Water reducingadmixtures can be used to optimize a mix by reducingcement and water requirements while stillretaining adequate workability for proper compactionof the concrete by the machine. Air entrainmentadmixtures are not effective in the drymix concrete. With the low water-cement ratiosand compaction placing method, air is difficult todisperse well and maintain.

Advantages of Hollow Core Slabs

Hollow core slabs are most widely known for

providing economical, efficient floor and roof

systems. The top surface can be prepared for the

installation of a floor covering by feathering the

joints with a latex cement, installing non-structural

fill concretes ranging from 1/2 in to 2 in (13 - 51

mm) thick depending on the material used, or by

casting a composite structural concrete topping.

The underside can be used as a finished ceiling as

installed, by painting, or by applying an acoustical

spray.

When properly coordinated for alignment, the

voids in a hollow core slabmay be used for electrical

or mechanical runs. For example, routing of a

lighting circuit through the cores can allow fixtures

in an exposed slab ceiling without unsightly

surface mounted conduit. Slabs used as the heated

mass in a passive solar application can be detailed

to distribute the heated air through the cores.

Structurally, a hollow core slab provides the efficiency

of a prestressed member for load capacity,

span range, and deflection control. In addition,

a basic diaphragm is provided for resisting

lateral loads by the grouted slab assembly provided

proper connections and details exist. A detailed

discussion of diaphragm capabilities is

presented in Chapter 4.

Excellent fire resistance is another attribute of

the hollow core slab. Depending on thickness and

strand cover, ratings up to a 4 hour endurance can

be achieved. Afire rating is dependent on equivalent

thickness for heat transmission, concrete cover

over the prestressing strands for strength in a

high temperature condition, and end restraint.

Underwriters Laboratories publishes fire ratings

for various assemblies. However, many building

codes allow a rational design procedure for

strength in a fire. This procedure, described in detail

in Chapter 6, considers strand temperature in

calculating strength. Required fire ratings should

be clearly specified in the contract documents.

Also, the fire rating should be considered in determining

the slab thickness to be used in preliminary

design.

Used as floor-ceiling assemblies, hollow core

slabs have the excellent sound transmission characteristics associated with concrete. The SoundTransmission Class rating ranges from about 47 to57 without topping and the Impact InsulationClass rating starts at about 23 for a plain slab andmay be increased to over 70 with the addition ofcarpeting and padding. Detailed information onthe acoustical properties of hollow core slabs ispresented in Chapter 7.

Prestressed wall panel

Pre-stressed concrete wall panels are a construction system widely used throughout Europe. Wall panels are pre-stressed and so this allows you maximum strength with minimum wall thickness.

Wall panels have a wide range of applications and are particularly suitable for industrial units, storage units, bulk grain stores, large sheds, general warehousing, earth retaining walls, compost and waste storage etc.

All our wall panels are manufactured in accordance with BS 8110 and BS 5502.

All of our products are CE certified

Prestressed Wall panels have a wide range of applications

and are particularly suitable for:

Industrial units

Storage units

Bulk grain stores

Large sheds

General warehousing

Earth retaining walls

Compost and waste storage

Prestressed Concrete Wall Panels are ready for immediate use once installed. These Wall Panels have significant advantages over traditional methods including;

Cost saving

Durability

Quality Finish

Easily cleaned

Wall Panels are supported by steel columns

Rapid Build. Typically up to 200m2 per day.

No builders or plasterers required.

No scaffold required.

No waste.

Panels can be installed regardless of weather conditions.

Panels can be removed or repositioned to meet changing circumstances.

Advantages

Prestressed Concrete Wall Panels are ready for immediate use once installed. These Wall Panels have significant advantages over traditional methods including;

Drumderry’s Wall Panels are the best choice for Commercial / Industrial applications. Each wall unit is manufactured to various sizes. Cast under controlled factory conditions, Precast Concrete Wall Panels provide a solid, secure and safe method of building when compared with traditional wall construction methods.

Advantagesof using Drumderry’s Precast Wall Panels include cost efficiency, speedy installation, durability, quality, fire resistance, thermal efficiency and low maintenance.

PRESTRESSED WALL PANELS have significant advantages over competing ordinary reinforcedpanels. The high strength prestressed panels have much higher resistance to loading and crackingwith the added advantage of flexibity under load.QUALITY – Manufactured to optimum standards with the highest quality raw materials. The 50Nconcrete mix, produced in a modern state-of-the-art batching plant, ensures strong robust wallssuitable for a variety of applications.VERSATLITY – The wide range of sizes and depths available allows a variety of applications.Panels can be easily moved and installed in another location. Double and Single load bearing available.MADE TO MEASURE – Panels can be made to order, each one individually labeled making themeasy to identify when installing.SPEED OF INSTALLATION – Panels are delivered to site ready for immediate use. High speed erectionensures substantial savings in labour costs. Each panel has 2 sockets cast into the tongue to facilitatea threaded loop when installing. Panels are chamfered along the ends to facilitate a place for sealerif required.FIXING OPTIONSPanels can be fitted to the RSJ/Beam in 3 ways:

1. Bolted to the inside face.

2. Slotted in between.

3. Bolted to outside face.