Monday, May 30, 2011

Two roles of mortar

I enjoy talking to experienced older masons.

I remember one guy in particular, who took an interest in my triangular block system.  He was thinking about mortar, and shared this with me:  “Mortar does two things.  It keeps blocks together and it keeps them apart.”

Mortar glues concrete blocks together, and it also keeps them from touching each other.  When blocks touch each other, they are more susceptible to cracking.  Mortar acts as a damper between blocks.

It keeps them together and keeps them apart.

Saturday, May 28, 2011

Typhoons and nuclear reactors

I’ve posted a few times on this blog about using the masonry system I’ve described as a potential solution for containment and protection for nuclear reactors. I discussed this here, here, here and here.

Japan’s Fukushima nuclear reactors remain vulnerable following the massive earthquake and tsunami which left these facilities crippled and leaking radiation to the outside.

Currently there is a typhoon bearing down on Japan, and eyes are on the Fukushima nuclear reactors. This facility is not ready for this level of weather assault.  The engineers are spraying a "dust inhibitor" material to try to prevent spread of contamination from leaked radiation.  Wouldn't you rather have a masonry shell containing radiation, than a loose, sprayed-on dust inhibitor?  This seems like a very poor approach for such a potentiually dangerous situation.

I am compelled to state again that the masonry system I’ve been describing is an appropriate solution for both containment of radioactive material and protection from outside forces; including tsunamis, typhoons, tornadoes, hurricanes, terrorists, etc. As has been discussed on this blog, the proposed solution creates a hardened structure capable of withstanding these forces.

The safety factor for the containment/protective shell can be increased by several factors simply by adding concentric shells of the interlocking masonry system, which can also be woven together with steel cable or other tensile elements (e.g., Kevlar, etc.).

I’ve been approached by consortiums concerned with cleaning up Japan, and making the nation safer from these catastrophic natural events: tsunamis, typhoons, etc. The system described on this blog remains a viable solution, and the time to fix things is now.

My thoughts are with the people of Japan, and I hope your country will get through this approaching typhoon without any more serious damage at Fukushima Daiichi.   Japan needs the third little pig!  They could let that typhoon huff and puff all it wants, without worry.

Monday, May 9, 2011

Never lost a load

One summer I worked as a dispatcher for LC Whitford, concrete products. I wanted to learn more about concrete from this summer job.

There was a fleet of around a dozen trucks. If someone called for concrete, I’d give them what they needed, make sure they were getting the right mix for their job, arrange delivery, make sure the weather was going to be acceptable, and get proper directions for the driver.

I did all the invoicing. Sometimes I’d have to interpret weather radar to anticipate when this or that shower would pass, and time the concrete delivery around the usual summer afternoon drifting dance of thunderstorms.

The fun part was casting huge steel reinforced concrete beams for various highway jobs. This was done just outside my dispatcher office window, and I enjoyed watching it. Around ten full trucks of concrete to cast one beam. Then they pick it up and move it with this crazy Dr. Seuss machine, after it cures some.

I worked with a good crew. I learned a lot. It was a good experience.

I was paid $6.00 per hour.

I never lost a load.

Sunday, May 8, 2011

Adding super-plasticizers to concrete

Plasticizers and super-plasticizers are sometimes added to concrete mix. Why is this done?

Concrete is a mixture of aggregate (rocks), sand, Portland cement, and water. Water combines with cement to form hydration products, which glue the mix together.

Portland cement has an electrostatic attraction to itself. It tends to stick or clump together when water is added. If cement is not dispersed in the concrete mix, but is stuck together in balls and clumps, then the concrete will be weakened. It is important to evenly disperse the cement for a mix to approach its potential strength.

Plasticizers (often called super-plasticizers) are chemical admixtures which cut the electrostatic attraction in cement . This allows the cement to become more evenly dispersed in the concrete mix, and creates a stronger concrete as a result.

Another significant benefit to using a super-plasticizer is the increased workability of the concrete. The mix doesn’t stick together so much; it is more fluid and liquid, without adding more water (too much water weakens concrete substantially).  Superplasticizers make the work of screeding and floating the poured concrete much easier, without using too much water.

Super-plasticizers are relatively inexpensive, and contribute significantly toward making better concrete.

Friday, May 6, 2011

Adding fiber to concrete

Fibers are sometimes added to concrete mix. Why is this done?

Concrete is a mixture of aggregate (rocks), sand , Portland cement, and water. Water combines with cement to form hydration products, which glue the mix together.

Upon initial set, there is a volume shrinkage of the cement paste. This small shrinkage may result in micro-cracks; tiny little flaws on the surface of the curing concrete. These cracks occur because wet cement paste has a low tensile strength, and cannot resist the small shrinkage from the initial cure.

Once cement has cured, it forms a brittle material. When any brittle material cracks, it always begins cracking at a small surface flaw, such as those produced on initial set, due to weak cement paste shrinkage. If these micro-cracks can be eliminated, a much stronger and longer-lived concrete is produced.

Micro fibers have a tendril-like structure, where tiny little spirals come out of a larger fiber (commonly polypropylene). When properly mixed, this type of fiber provides anchorage and locking into a wet cement paste. It will provide the necessary tensile strength for the wet cement paste to resist micro-cracking from shrinkage on initial set.  This results in a much stronger and tougher concrete.

Fiber added to concrete mix reduces the workability of the wet concrete to a small degree. It can be difficult to float a surface due to the fibers.

The specifications for fiber concrete show no increase in tensile strength, but those who really know concrete realize that these microfibers provide an actual slight increase in tensile strength of concrete, and also increase its toughness (resistance to crack propagation). Fibered concrete is a little tougher and has more flexural rigidity.

Fiber added to concrete mix makes a better concrete.

Tuesday, May 3, 2011

Containment and Protection

In three previous entries I wrote of using the masonry system described on this blog as a containment structure for a nuclear reactor; here, here, and here.

In these entries I discussed the importance of providing an adequate containment structure as a safety factor in the event of a nuclear accident. An inadequate containment structure will allow dangerous radiation to leak to the outside, as has happened in Chernobyl and Fukushima Daiichi.

In addition to providing containment of radiation, a properly designed and built containment structure will help to protect the nuclear reactor from any dangerous forces outside the reactor. It will serve as both containment from inside the reactor and a shield from outside the reactor. This is an important and often overlooked safety consideration.

Potential threats from outside a reactor range from hurricanes and typhoons to tsunamis and even terrorists. A toughened, hardened, robust, blast-resistant shell can help protect a nuclear reactor from storms, explosions, tsunamis, airplanes, etc. This safety factor is provided in addition to the feature of containment. That is, a properly installed shell will both prevent escape of any leaked radiation and will also protect the reactor from outside forces at the same time.