Strength of 1960 heydite block and grout 1

[whir]

I have a simple design of a safety rail being mounted on a roof next to a piece of equipment. The posts of the rail penetrate the roof and will be mounted to the inside face of the masonry bearing wall below. The moment on the rail post will be taken by a masonry anchor at the bottom of the post. The wall is heydite block from about 1960. Does anyone know what the strength of that block might be and what the strength of typical grout was at that time? I was just going to assume 1500 psi, but I don't have much knowledge of that time period.

 

[concretemasonry]

The strength, f'm, if that is what you are referring to will depend on what was made 50 years ago. The prism strength (f'm) is intended to be a measure of the structural element (the wall)and not the measure of some small part or raw material.

You referred to "heydite block". Just a guess that it is a lightweight block using some type of lightweight aggregate is just a raw material that is used by manufacturers. The real "Haydite" is an expanded shale or slate material good lightweight aggregate. It had a good reputation and very often all lightweight block were referred to as "haydite block" Normally, a block is made using varying percentages oif various aggregates (3/8" minus stone, natural heavyweight sand and lightweight aggregate of some manufacture) and possibly slag or cinders in some areas, but they were very regional. Lightweight, medium weight and normal weight block all had to meet the same ASTM requirements (ASTM C90)for strength.

Since the process of hydration continues long before the block are out of the plant, strengths could possibly be much higher. I have seen 4800 psi hollow (ungrouted) block prism strengths from prisms that were made using 2200 - 2500 psi mortar.

Because of the manufacturing process at that time the block generally had enough strength to surpass the minimal ASTM C90 requirements. Undoubtedly, the block, mortar, grout (if any) have gained substantial strength unless the wall was subjected to severe weathering or chemical attack.

Ultimately, the strength of the anchored post will depend on the method of attachment to the face and whether there is any grout or reinforcement. At the top of most walls, there is a bond beam that consists of a special block filled with reinforcement and grout to provide continuity and uniform distribution of vertical loads. There also may be prescriptive vertical reinforcement that in grouted cells.

Your assumption of a 1500 psi f'm strength should be conservative since it is what you would assume today, although the actual strength would probably be higher due to improvements in controls and manufacturing techniques and not real changes in material ASTM specifications for more that 50 years. I would be prudent to make sure the connection method is adequate to transfer the loads to the existing wall.

Dick

Engineer and international traveler interested in construction techniques, problems and proper design.

 

[whir]

Thanks for the information. Looking at the drawings, I find reinforcing called out for the concrete, but the wall just has a label that calls out haydite block. No mention of reinforcing or grout. It appears that he was confident that the builder knew how to build a haydite wall.