I continue to be intrigued by the way that “ridiculous” elements in the Book of Mormon eventually become significant evidences of authenticity. The mention of cement in Helaman 3 is a case in point. I’ve mentioned this before, but it’s worth remembering. Here is an excerpt from my Book of Mormon Evidences page:
In 1929, Heber J. Grant (former President of the Church) told the story of a man with a doctorate who had ridiculed him for believing in the Book of Mormon. That learned man cited the mention of cement work as an obvious lie “because the people in that early age knew nothing about cement.” President Grant, who was a young man at the time of that conversation, said:
“That does not affect my faith one particle. I read the Book of Mormon prayerfully and supplicated God for a testimony in my heart and soul of the divinity of it, and I have accepted it and believe it with all my heart.” I also said to him, “If my children do not find cement houses, I expect that my grandchildren will.” He said, “Well, what is the good of talking with a fool like that?” (April 1929 Conference Report, p. 128 ff.)
President Grant’s statement was prophetic. Today, tourists to Mesoamerica can find ancient cement work in abundance at Teotihuacan (which is clearly “in the land north” according to modern models for Book of Mormon geography). Mesoamerican cement was being used at least by the first century B.C. (David A. Palmer, In Search of Cumorah, Horizon Publishers, Bountiful, UT, 1981, p. 121). Palmer shows a photograph of cement used to surface a temple at the Chiapa de Corzo site. Palmer also cites Monte Alban, which is south of Teotihuacan but still in the “land north,” as another example of ancient cement work. Several examples of cement work use tiny volcanic stones (0.5 to 2 mm diameter) mixed with clay and lime to produce the cement. Cement was also used in the ancient city of Kaminaljuyu (modern Guatemala City).
Mesoamerican work with cement involved more than merely applying a veneer to buildings. Important structural elements were made with cement, and the use of cement in Mesoamerica dates to about the time when the Book of Mormon reports its development (46 B.C.). John Welch provides further data in his article, “A Steady Stream of Significant Recognitions” in Echoes and Evidences of the Book of Mormon, ed. D.W. Parry, D.C. Peterson, and J.W. Welch (Provo, Utah: FARMS, 2002), pp. 372-374:
No one in the nineteenth century could have known that cement, in fact, was extensively used in Mesoamerica beginning largely at this time, the middle of the first century B.C.
One of the most notable uses of cement is in the temple complex at Teotihuacan, north of present-day Mexico City. According to David S. Hyman, the structural use of cement appears suddenly in the archaeological record. And yet its earliest sample “is a fully developed product.” The cement floor slabs at this site “were remarkably high in structural quality.” Although exposed to the elements for nearly two thousand years, they still “exceed many present-day building code requirements.”  This is consistent with the Book of Mormon record, which treats this invention as an important new development involving great skill and becoming something of a sensation.
After this important technological breakthrough, cement was used at many sites in the Valley of Mexico and in the Maya regions of southern Mexico, Guatemala, and Honduras, which very well may have been close to the Nephite heartlands. Cement was used in the later construction of buildings at such sites as Cerro de Texcotzingo, Tula, Palenque, Tikal, Copan, Uxmal, and Chichen Itza. Further, the use of cement is “a Maya habit, absent from non-Maya examples of corbelled vaulting from the southeastern United States to southern South America.” 
Mesoamerican cement was almost exclusively lime cement. The limestone was purified on a “cylindrical pile of timber, which requires a vast amount of labor to cut and considerable skill to construct in such a way that combustion of the stone and wood is complete and a minimum of impurities remains in the product.”  The fact that very little carbon is found in this cement once again “attests to the ability of these ancient peoples.” 
John Sorenson has further noted the expert sophistication in the use of cement at El Tajin, east of Mexico City, in the centuries following Book of Mormon times. Cement roofs covered sizable areas: “Sometimes the builders filled a room with stones and mud, smoothed the surface on top to receive the concrete, then removed the interior fill when the [slab] on top had dried.” 
Footnotes for the above passage:
1. See Matthew G. Wells and John W. Welch, “Concrete Evidence for the Book of Mormon,” Insights (May 1991): 2.
2. David S. Hyman, A Study of the Calcareous Cements in Prehispanic Mesoamerican Building Construction (Baltimore: Johns Hopkins University, 1970), ii, sec. 6, p. 7.
3. George Kubler, The Art and Architecture of Ancient America, 2nd ed. (Baltimore: Penguin, 1975), 201, emphasis added.
4. Tatiana Proskouriakoff, An Album of Maya Architecture (Norman: University of Oklahoma Press, 1963), xv.
5. Hyman, A Study of the Calcareous Cements, sec. 6, p. 5.
6. John L. Sorenson, “Digging into the Book of Mormon,” Ensign, October 1984, 19.