February 1993 Table of Contents

Features Placing and Vibrating Poured Concrete Walls

Reduce cold joints, honeycombing, and bugholes by training workers how to place and vibrate concrete in walls. The basic principles of placement and vibration are the same for any placing equipment used. If problems occur, however, corrective action can minimize their recurrence. Read more

Features French Use Slipform Pavers in Eurotunnel

A joint English and French project involved boring three tunnels through 31 miles of a chalk marl formation to link the cities of Dover and Calais. Two tunnels will accommodate high-speed trains; the third will be a service tunnel. The tunnels are lined with precast concrete ring segments. The bases for the tunnel rail bed and two sidewalks (one for evacuation and one for maintenance) are paved with concrete. Read more

Features Applying Waterproofing Sheets to Below-Grade Walls

Sheet membranes have many benefits Read more

Features Joints in Poured Walls

Though concrete has a tendency to crack and does crack in most cases, cracks can be controlled by joints, or planned separations in concrete. Cast-in place concrete walls use three types of joints. Read more

Features Air Bubbles in Fresh Concrete

Air bubbles added to fresh concrete improve workability and frost resistance. Frost-resistant concrete requires an adequate number and volume of closely spaced, microscopic air voids. This is best accomplished with a minimum total air content and minimum impact on strength provided by a fine gradation of air voids. Read more

Features Shotcrete Pumps and Related Equipment

In the dry-mix shotcrete process, dry blended mix materials are delivered through a line or hose to a nozzle, where water is added. There are two distinct types of dry-mix shotcrete equipment: single- and double-chamber pumps, and continuous-feed or rotary pumps which come in two types: barrel and feed bowl. Read more

Features Can You Use Plywood Forms Without Oiling?

Panels with a 4-mil-thick, hard polymeric resin coating applied to exterior-grade plywood require no release agent. These are 4x8-foot panels bonded by waterproof glue and sealed at the edges to prevent moisture penetration. Read more

Problem Clinic Adding Chlorides for Flatwork Mix

Our standard flatwork mix is six-bag, 3/4-inch limestone, with 6% air and 1 1/2 pounds of polypropylene fibers. It is placed at a slump of 4 inches. When ambient temperatures dictate, we use a maximum of 1% calcium chloride. Adding the chloride at the rea Read more

Problem Clinic Cleaning White Concrete

We need to remove hardened construction adhesive from a new white concrete surface. We've tried grinding, but the material melts. Any other suggestions? Read more

Problem Clinic Slump Loss and Mix Water Content

We need to submit a concrete mix to be placed by pump. Slump and air are specified at the point of placement. Can we increase the initial mix water content to compensate for water lost in pumping and also satisfy the limit on water-cement ratio at the poi Read more

Problem Clinic Footing Elevations

What is the tolerance for elevations on cast-in-place concrete footings? Read more

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